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 $64.42   11.551%   $71.8612   $71.86   $71.85   $71.90  
  Purchase #2 $65.68   4.595%   $68.698   $68.70   $68.70   $68.70  
  Purchase #3 $126.58   8.165%   $136.9153   $136.92   $136.90   $136.90  
  Purchase #4 $105.52   4.175%   $109.9255   $109.93   $109.95   $109.90  
  Purchase #5 $31.59   6.873%   $33.7612   $33.76   $33.75   $33.80  
  Purchase #6 $35.59   6.373%   $37.8582   $37.86   $37.85   $37.90  
  Purchase #7 $23.67   10.590%   $26.1767   $26.18   $26.20   $26.20  
  7 purchase totals = $453.05       $485.1961   $485.21   $485.20   $485.30