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 $228.52   10.606%   $252.7568   $252.76   $252.75   $252.80  
  Purchase #2 $125.53   5.694%   $132.6777   $132.68   $132.70   $132.70  
  Purchase #3 $151.59   3.490%   $156.8805   $156.88   $156.90   $156.90  
  Purchase #4 $185.27   11.825%   $207.1782   $207.18   $207.20   $207.20  
  Purchase #5 $61.89   9.832%   $67.975   $67.98   $68.00   $68.00  
  Purchase #6 $250.66   8.116%   $271.0036   $271.00   $271.00   $271.00  
  Purchase #7 $69.28   3.240%   $71.5247   $71.52   $71.50   $71.50  
  7 purchase totals = $1,072.74       $1,159.9965   $1,160.00   $1,160.05   $1,160.10