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 $36.48   5.120%   $38.3478   $38.35   $38.35   $38.30  
  Purchase #2 $177.93   9.516%   $194.8618   $194.86   $194.85   $194.90  
  Purchase #3 $197.47   13.537%   $224.2015   $224.20   $224.20   $224.20  
  Purchase #4 $236.91   8.496%   $257.0379   $257.04   $257.05   $257.00  
  Purchase #5 $58.74   6.495%   $62.5552   $62.56   $62.55   $62.60  
  Purchase #6 $146.85   9.526%   $160.8389   $160.84   $160.85   $160.80  
  Purchase #7 $241.65   11.401%   $269.2005   $269.20   $269.20   $269.20  
  7 purchase totals = $1,096.03       $1,207.0436   $1,207.05   $1,207.05   $1,207.00