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 $22.88   11.511%   $25.5137   $25.51   $25.50   $25.50  
  Purchase #2 $8.53   5.213%   $8.9747   $8.97   $8.95   $9.00  
  Purchase #3 $210.77   8.193%   $228.0384   $228.04   $228.05   $228.00  
  Purchase #4 $134.95   12.811%   $152.2384   $152.24   $152.25   $152.20  
  Purchase #5 $90.79   8.213%   $98.2466   $98.25   $98.25   $98.20  
  Purchase #6 $226.74   13.689%   $257.7784   $257.78   $257.80   $257.80  
  Purchase #7 $112.47   12.317%   $126.3229   $126.32   $126.30   $126.30  
  7 purchase totals = $807.13       $897.1131   $897.11   $897.10   $897.00