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 $54.37   4.147%   $56.6247   $56.62   $56.60   $56.60  
  Purchase #2 $104.29   8.518%   $113.1734   $113.17   $113.15   $113.20  
  Purchase #3 $183.76   5.366%   $193.6206   $193.62   $193.60   $193.60  
  Purchase #4 $68.74   7.424%   $73.8433   $73.84   $73.85   $73.80  
  Purchase #5 $167.79   3.316%   $173.3539   $173.35   $173.35   $173.40  
  Purchase #6 $241.76   10.184%   $266.3808   $266.38   $266.40   $266.40  
  Purchase #7 $245.37   8.460%   $266.1283   $266.13   $266.15   $266.10  
  7 purchase totals = $1,066.08       $1,143.1250   $1,143.11   $1,143.10   $1,143.10