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 $214.43   13.778%   $243.9742   $243.97   $243.95   $244.00  
  Purchase #2 $141.75   12.421%   $159.3568   $159.36   $159.35   $159.40  
  Purchase #3 $240.60   8.432%   $260.8874   $260.89   $260.90   $260.90  
  Purchase #4 $229.57   4.337%   $239.5265   $239.53   $239.55   $239.50  
  Purchase #5 $88.92   12.635%   $100.155   $100.16   $100.15   $100.20  
  Purchase #6 $170.42   8.605%   $185.0846   $185.08   $185.10   $185.10  
  Purchase #7 $195.33   8.281%   $211.5053   $211.51   $211.50   $211.50  
  7 purchase totals = $1,281.02       $1,400.4898   $1,400.50   $1,400.50   $1,400.60