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 $106.68   12.181%   $119.6747   $119.67   $119.65   $119.70  
  Purchase #2 $197.42   6.649%   $210.5465   $210.55   $210.55   $210.50  
  Purchase #3 $72.74   5.561%   $76.7851   $76.79   $76.80   $76.80  
  Purchase #4 $17.45   11.327%   $19.4266   $19.43   $19.45   $19.40  
  Purchase #5 $86.67   12.753%   $97.723   $97.72   $97.70   $97.70  
  Purchase #6 $223.65   10.874%   $247.9697   $247.97   $247.95   $248.00  
  Purchase #7 $223.92   7.212%   $240.0691   $240.07   $240.05   $240.10  
  7 purchase totals = $928.53       $1,012.1947   $1,012.20   $1,012.15   $1,012.20