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 $34.94   5.782%   $36.9602   $36.96   $36.95   $37.00  
  Purchase #2 $216.67   8.473%   $235.0284   $235.03   $235.05   $235.00  
  Purchase #3 $244.27   9.351%   $267.1117   $267.11   $267.10   $267.10  
  Purchase #4 $195.70   13.502%   $222.1234   $222.12   $222.10   $222.10  
  Purchase #5 $50.59   10.571%   $55.9379   $55.94   $55.95   $55.90  
  Purchase #6 $41.63   3.496%   $43.0854   $43.09   $43.10   $43.10  
  Purchase #7 $6.59   4.683%   $6.8986   $6.90   $6.90   $6.90  
  7 purchase totals = $790.39       $867.1456   $867.15   $867.15   $867.10