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 $65.49   9.497%   $71.7096   $71.71   $71.70   $71.70  
  Purchase #2 $56.75   6.626%   $60.5103   $60.51   $60.50   $60.50  
  Purchase #3 $68.55   8.439%   $74.3349   $74.33   $74.35   $74.30  
  Purchase #4 $48.87   10.807%   $54.1514   $54.15   $54.15   $54.20  
  Purchase #5 $248.68   7.174%   $266.5203   $266.52   $266.50   $266.50  
  Purchase #6 $219.55   7.577%   $236.1853   $236.19   $236.20   $236.20  
  Purchase #7 $41.54   9.196%   $45.36   $45.36   $45.35   $45.40  
  7 purchase totals = $749.43       $808.7718   $808.77   $808.75   $808.80