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 $250.87   8.308%   $271.7123   $271.71   $271.70   $271.70  
  Purchase #2 $222.82   4.331%   $232.4703   $232.47   $232.45   $232.50  
  Purchase #3 $53.59   8.417%   $58.1007   $58.10   $58.10   $58.10  
  Purchase #4 $114.52   6.871%   $122.3887   $122.39   $122.40   $122.40  
  Purchase #5 $230.96   6.725%   $246.4921   $246.49   $246.50   $246.50  
  Purchase #6 $247.47   10.228%   $272.7812   $272.78   $272.80   $272.80  
  Purchase #7 $249.43   7.598%   $268.3817   $268.38   $268.40   $268.40  
  7 purchase totals = $1,369.66       $1,472.3270   $1,472.32   $1,472.35   $1,472.40