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 $87.28   10.858%   $96.7569   $96.76   $96.75   $96.80  
  Purchase #2 $101.68   11.409%   $113.2807   $113.28   $113.30   $113.30  
  Purchase #3 $195.66   3.355%   $202.2244   $202.22   $202.20   $202.20  
  Purchase #4 $141.61   10.183%   $156.0301   $156.03   $156.05   $156.00  
  Purchase #5 $175.64   7.236%   $188.3493   $188.35   $188.35   $188.30  
  Purchase #6 $72.64   3.747%   $75.3618   $75.36   $75.35   $75.40  
  Purchase #7 $8.72   13.217%   $9.8725   $9.87   $9.85   $9.90  
  7 purchase totals = $783.23       $841.8757   $841.87   $841.85   $841.90