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 $249.41   5.327%   $262.6961   $262.70   $262.70   $262.70  
  Purchase #2 $118.61   4.524%   $123.9759   $123.98   $124.00   $124.00  
  Purchase #3 $50.70   3.424%   $52.436   $52.44   $52.45   $52.40  
  Purchase #4 $162.47   4.472%   $169.7357   $169.74   $169.75   $169.70  
  Purchase #5 $152.97   4.579%   $159.9745   $159.97   $159.95   $160.00  
  Purchase #6 $134.96   13.791%   $153.5723   $153.57   $153.55   $153.60  
  Purchase #7 $90.82   12.545%   $102.2134   $102.21   $102.20   $102.20  
  7 purchase totals = $959.94       $1,024.6039   $1,024.61   $1,024.60   $1,024.60