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 $124.62   13.250%   $141.1322   $141.13   $141.15   $141.10  
  Purchase #2 $236.28   11.161%   $262.6512   $262.65   $262.65   $262.70  
  Purchase #3 $38.80   7.862%   $41.8505   $41.85   $41.85   $41.90  
  Purchase #4 $44.99   4.492%   $47.011   $47.01   $47.00   $47.00  
  Purchase #5 $19.90   11.816%   $22.2514   $22.25   $22.25   $22.30  
  Purchase #6 $105.72   10.764%   $117.0997   $117.10   $117.10   $117.10  
  Purchase #7 $195.55   11.412%   $217.8662   $217.87   $217.85   $217.90  
  7 purchase totals = $765.86       $849.8622   $849.86   $849.85   $850.00