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 $105.67   12.743%   $119.1355   $119.14   $119.15   $119.10  
  Purchase #2 $130.68   4.344%   $136.3567   $136.36   $136.35   $136.40  
  Purchase #3 $88.86   12.238%   $99.7347   $99.73   $99.75   $99.70  
  Purchase #4 $52.25   6.578%   $55.687   $55.69   $55.70   $55.70  
  Purchase #5 $229.52   4.745%   $240.4107   $240.41   $240.40   $240.40  
  Purchase #6 $24.63   7.159%   $26.3933   $26.39   $26.40   $26.40  
  Purchase #7 $177.77   6.557%   $189.4264   $189.43   $189.45   $189.40  
  7 purchase totals = $809.38       $867.1443   $867.15   $867.20   $867.10