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 $45.97   10.446%   $50.772   $50.77   $50.75   $50.80  
  Purchase #2 $217.26   3.359%   $224.5578   $224.56   $224.55   $224.60  
  Purchase #3 $33.50   5.417%   $35.3147   $35.31   $35.30   $35.30  
  Purchase #4 $246.61   10.279%   $271.959   $271.96   $271.95   $272.00  
  Purchase #5 $164.25   11.323%   $182.848   $182.85   $182.85   $182.80  
  Purchase #6 $71.58   6.136%   $75.9721   $75.97   $75.95   $76.00  
  Purchase #7 $233.71   12.326%   $262.5171   $262.52   $262.50   $262.50  
  7 purchase totals = $1,012.88       $1,103.9407   $1,103.94   $1,103.85   $1,104.00