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 $29.48   12.774%   $33.2458   $33.25   $33.25   $33.20  
  Purchase #2 $10.48   7.774%   $11.2947   $11.29   $11.30   $11.30  
  Purchase #3 $116.89   7.757%   $125.9572   $125.96   $125.95   $126.00  
  Purchase #4 $220.87   5.709%   $233.4795   $233.48   $233.50   $233.50  
  Purchase #5 $129.38   9.599%   $141.7992   $141.80   $141.80   $141.80  
  Purchase #6 $167.84   11.676%   $187.437   $187.44   $187.45   $187.40  
  Purchase #7 $218.51   4.796%   $228.9897   $228.99   $229.00   $229.00  
  7 purchase totals = $893.45       $962.2031   $962.21   $962.25   $962.20