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 $232.27   10.202%   $255.9662   $255.97   $255.95   $256.00  
  Purchase #2 $58.34   11.210%   $64.8799   $64.88   $64.90   $64.90  
  Purchase #3 $185.55   6.697%   $197.9763   $197.98   $198.00   $198.00  
  Purchase #4 $226.71   3.442%   $234.5134   $234.51   $234.50   $234.50  
  Purchase #5 $38.51   4.265%   $40.1525   $40.15   $40.15   $40.20  
  Purchase #6 $147.71   10.491%   $163.2063   $163.21   $163.20   $163.20  
  Purchase #7 $134.83   12.698%   $151.9507   $151.95   $151.95   $152.00  
  7 purchase totals = $1,023.92       $1,108.6453   $1,108.65   $1,108.65   $1,108.80