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 $87.95   6.865%   $93.9878   $93.99   $94.00   $94.00  
  Purchase #2 $172.93   11.701%   $193.1645   $193.16   $193.15   $193.20  
  Purchase #3 $177.72   13.679%   $202.0303   $202.03   $202.05   $202.00  
  Purchase #4 $70.71   7.239%   $75.8287   $75.83   $75.85   $75.80  
  Purchase #5 $150.73   5.734%   $159.3729   $159.37   $159.35   $159.40  
  Purchase #6 $114.54   3.733%   $118.8158   $118.82   $118.80   $118.80  
  Purchase #7 $147.68   9.287%   $161.395   $161.40   $161.40   $161.40  
  7 purchase totals = $922.26       $1,004.5950   $1,004.60   $1,004.60   $1,004.60