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 $32.25   13.820%   $36.707   $36.71   $36.70   $36.70  
  Purchase #2 $24.62   12.614%   $27.7256   $27.73   $27.75   $27.70  
  Purchase #3 $226.62   5.754%   $239.6597   $239.66   $239.65   $239.70  
  Purchase #4 $225.92   5.293%   $237.8779   $237.88   $237.90   $237.90  
  Purchase #5 $147.34   13.796%   $167.667   $167.67   $167.65   $167.70  
  Purchase #6 $187.47   13.352%   $212.501   $212.50   $212.50   $212.50  
  Purchase #7 $10.85   9.347%   $11.8641   $11.86   $11.85   $11.90  
  7 purchase totals = $855.07       $934.0023   $934.01   $934.00   $934.10