Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $179.59   12.612%   $202.2399   $202.24   $202.25   $202.20  
  Purchase #2 $242.79   9.639%   $266.1925   $266.19   $266.20   $266.20  
  Purchase #3 $214.90   5.871%   $227.5168   $227.52   $227.50   $227.50  
  Purchase #4 $125.73   12.696%   $141.6927   $141.69   $141.70   $141.70  
  Purchase #5 $175.43   5.363%   $184.8383   $184.84   $184.85   $184.80  
  Purchase #6 $116.36   13.485%   $132.0511   $132.05   $132.05   $132.10  
  Purchase #7 $230.69   11.406%   $257.0025   $257.00   $257.00   $257.00  
  7 purchase totals = $1,285.49       $1,411.5338   $1,411.53   $1,411.55   $1,411.50