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 $191.56   8.523%   $207.8867   $207.89   $207.90   $207.90  
  Purchase #2 $189.78   7.116%   $203.2847   $203.28   $203.30   $203.30  
  Purchase #3 $61.55   7.697%   $66.2875   $66.29   $66.30   $66.30  
  Purchase #4 $32.49   4.437%   $33.9316   $33.93   $33.95   $33.90  
  Purchase #5 $146.89   9.288%   $160.5331   $160.53   $160.55   $160.50  
  Purchase #6 $33.70   3.860%   $35.0008   $35.00   $35.00   $35.00  
  Purchase #7 $58.70   10.330%   $64.7637   $64.76   $64.75   $64.80  
  7 purchase totals = $714.67       $771.6881   $771.68   $771.75   $771.70