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 $137.48   12.564%   $154.753   $154.75   $154.75   $154.80  
  Purchase #2 $215.68   7.561%   $231.9876   $231.99   $232.00   $232.00  
  Purchase #3 $21.27   11.618%   $23.7411   $23.74   $23.75   $23.70  
  Purchase #4 $162.46   4.593%   $169.9218   $169.92   $169.90   $169.90  
  Purchase #5 $153.45   3.206%   $158.3696   $158.37   $158.35   $158.40  
  Purchase #6 $145.94   7.181%   $156.42   $156.42   $156.40   $156.40  
  Purchase #7 $65.28   13.110%   $73.8382   $73.84   $73.85   $73.80  
  7 purchase totals = $901.56       $969.0313   $969.03   $969.00   $969.00