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 $116.86   8.701%   $127.028   $127.03   $127.05   $127.00  
  Purchase #2 $93.70   4.708%   $98.1114   $98.11   $98.10   $98.10  
  Purchase #3 $158.87   4.719%   $166.3671   $166.37   $166.35   $166.40  
  Purchase #4 $90.56   12.168%   $101.5793   $101.58   $101.60   $101.60  
  Purchase #5 $209.98   13.489%   $238.3042   $238.30   $238.30   $238.30  
  Purchase #6 $175.75   6.360%   $186.9277   $186.93   $186.95   $186.90  
  Purchase #7 $244.94   12.157%   $274.7174   $274.72   $274.70   $274.70  
  7 purchase totals = $1,090.66       $1,193.0351   $1,193.04   $1,193.05   $1,193.00