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 $187.80   8.545%   $203.8475   $203.85   $203.85   $203.80  
  Purchase #2 $24.39   6.391%   $25.9488   $25.95   $25.95   $25.90  
  Purchase #3 $83.59   8.573%   $90.7562   $90.76   $90.75   $90.80  
  Purchase #4 $169.73   10.234%   $187.1002   $187.10   $187.10   $187.10  
  Purchase #5 $90.56   6.316%   $96.2798   $96.28   $96.30   $96.30  
  Purchase #6 $178.39   3.651%   $184.903   $184.90   $184.90   $184.90  
  Purchase #7 $224.61   8.601%   $243.9287   $243.93   $243.95   $243.90  
  7 purchase totals = $959.07       $1,032.7642   $1,032.77   $1,032.80   $1,032.70