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 $48.79   12.541%   $54.9088   $54.91   $54.90   $54.90  
  Purchase #2 $77.92   4.867%   $81.7124   $81.71   $81.70   $81.70  
  Purchase #3 $19.40   8.161%   $20.9832   $20.98   $21.00   $21.00  
  Purchase #4 $215.97   6.564%   $230.1463   $230.15   $230.15   $230.10  
  Purchase #5 $113.30   8.234%   $122.6291   $122.63   $122.65   $122.60  
  Purchase #6 $236.43   11.808%   $264.3477   $264.35   $264.35   $264.30  
  Purchase #7 $212.85   3.750%   $220.8319   $220.83   $220.85   $220.80  
  7 purchase totals = $924.66       $995.5594   $995.56   $995.60   $995.40