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 $189.46   5.110%   $199.1414   $199.14   $199.15   $199.10  
  Purchase #2 $241.88   9.351%   $264.4982   $264.50   $264.50   $264.50  
  Purchase #3 $78.82   11.827%   $88.142   $88.14   $88.15   $88.10  
  Purchase #4 $161.86   4.618%   $169.3347   $169.33   $169.35   $169.30  
  Purchase #5 $96.62   7.850%   $104.2047   $104.20   $104.20   $104.20  
  Purchase #6 $139.82   11.148%   $155.4071   $155.41   $155.40   $155.40  
  Purchase #7 $14.84   3.804%   $15.4045   $15.40   $15.40   $15.40  
  7 purchase totals = $923.30       $996.1326   $996.12   $996.15   $996.00