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 $60.34   6.104%   $64.0232   $64.02   $64.00   $64.00  
  Purchase #2 $230.99   11.506%   $257.5677   $257.57   $257.55   $257.60  
  Purchase #3 $121.73   12.697%   $137.1861   $137.19   $137.20   $137.20  
  Purchase #4 $210.75   6.203%   $223.8228   $223.82   $223.80   $223.80  
  Purchase #5 $48.83   11.647%   $54.5172   $54.52   $54.50   $54.50  
  Purchase #6 $170.33   4.320%   $177.6883   $177.69   $177.70   $177.70  
  Purchase #7 $212.80   11.294%   $236.8336   $236.83   $236.85   $236.80  
  7 purchase totals = $1,055.77       $1,151.6389   $1,151.64   $1,151.60   $1,151.60