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 $29.59   10.634%   $32.7366   $32.74   $32.75   $32.70  
  Purchase #2 $144.29   8.725%   $156.8793   $156.88   $156.90   $156.90  
  Purchase #3 $183.56   11.832%   $205.2788   $205.28   $205.30   $205.30  
  Purchase #4 $167.72   12.105%   $188.0225   $188.02   $188.00   $188.00  
  Purchase #5 $188.87   11.543%   $210.6713   $210.67   $210.65   $210.70  
  Purchase #6 $236.69   5.688%   $250.1529   $250.15   $250.15   $250.20  
  Purchase #7 $64.31   13.559%   $73.0298   $73.03   $73.05   $73.00  
  7 purchase totals = $1,015.03       $1,116.7712   $1,116.77   $1,116.80   $1,116.80