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 $234.90   7.582%   $252.7101   $252.71   $252.70   $252.70  
  Purchase #2 $164.25   11.174%   $182.6033   $182.60   $182.60   $182.60  
  Purchase #3 $118.46   11.207%   $131.7358   $131.74   $131.75   $131.70  
  Purchase #4 $167.73   8.852%   $182.5775   $182.58   $182.60   $182.60  
  Purchase #5 $84.99   3.431%   $87.906   $87.91   $87.90   $87.90  
  Purchase #6 $95.90   7.265%   $102.8671   $102.87   $102.85   $102.90  
  Purchase #7 $132.69   4.223%   $138.2935   $138.29   $138.30   $138.30  
  7 purchase totals = $998.92       $1,078.6933   $1,078.70   $1,078.70   $1,078.70