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 $193.78   8.425%   $210.106   $210.11   $210.10   $210.10  
  Purchase #2 $65.87   6.807%   $70.3538   $70.35   $70.35   $70.40  
  Purchase #3 $69.62   13.622%   $79.1036   $79.10   $79.10   $79.10  
  Purchase #4 $189.57   8.369%   $205.4351   $205.44   $205.45   $205.40  
  Purchase #5 $68.56   5.167%   $72.1025   $72.10   $72.10   $72.10  
  Purchase #6 $173.77   12.762%   $195.9465   $195.95   $195.95   $195.90  
  Purchase #7 $167.33   9.418%   $183.0891   $183.09   $183.10   $183.10  
  7 purchase totals = $928.50       $1,016.1366   $1,016.14   $1,016.15   $1,016.10