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 $190.97   5.763%   $201.9756   $201.98   $202.00   $202.00  
  Purchase #2 $203.96   6.277%   $216.7626   $216.76   $216.75   $216.80  
  Purchase #3 $61.27   5.277%   $64.5032   $64.50   $64.50   $64.50  
  Purchase #4 $150.37   5.102%   $158.0419   $158.04   $158.05   $158.00  
  Purchase #5 $188.28   11.418%   $209.7778   $209.78   $209.80   $209.80  
  Purchase #6 $37.94   8.865%   $41.3034   $41.30   $41.30   $41.30  
  Purchase #7 $126.47   10.616%   $139.8961   $139.90   $139.90   $139.90  
  7 purchase totals = $959.26       $1,032.2606   $1,032.26   $1,032.30   $1,032.30