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 $32.78   13.578%   $37.2309   $37.23   $37.25   $37.20  
  Purchase #2 $64.40   5.572%   $67.9884   $67.99   $68.00   $68.00  
  Purchase #3 $168.84   3.111%   $174.0926   $174.09   $174.10   $174.10  
  Purchase #4 $204.97   9.488%   $224.4176   $224.42   $224.40   $224.40  
  Purchase #5 $58.58   9.867%   $64.3601   $64.36   $64.35   $64.40  
  Purchase #6 $243.29   5.532%   $256.7488   $256.75   $256.75   $256.70  
  Purchase #7 $81.83   11.156%   $90.959   $90.96   $90.95   $91.00  
  7 purchase totals = $854.69       $915.7974   $915.80   $915.80   $915.80