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 $201.70   11.190%   $224.2702   $224.27   $224.25   $224.30  
  Purchase #2 $166.97   11.354%   $185.9278   $185.93   $185.95   $185.90  
  Purchase #3 $217.68   7.796%   $234.6503   $234.65   $234.65   $234.70  
  Purchase #4 $27.65   6.558%   $29.4633   $29.46   $29.45   $29.50  
  Purchase #5 $201.30   13.762%   $229.0029   $229.00   $229.00   $229.00  
  Purchase #6 $69.29   9.816%   $76.0915   $76.09   $76.10   $76.10  
  Purchase #7 $31.43   6.455%   $33.4588   $33.46   $33.45   $33.50  
  7 purchase totals = $916.02       $1,012.8648   $1,012.86   $1,012.85   $1,013.00