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 $45.63   3.610%   $47.2772   $47.28   $47.30   $47.30  
  Purchase #2 $165.74   12.327%   $186.1708   $186.17   $186.15   $186.20  
  Purchase #3 $157.80   6.213%   $167.6041   $167.60   $167.60   $167.60  
  Purchase #4 $234.97   6.432%   $250.0833   $250.08   $250.10   $250.10  
  Purchase #5 $44.35   8.221%   $47.996   $48.00   $48.00   $48.00  
  Purchase #6 $224.50   5.217%   $236.2122   $236.21   $236.20   $236.20  
  Purchase #7 $83.48   6.562%   $88.958   $88.96   $88.95   $89.00  
  7 purchase totals = $956.47       $1,024.3016   $1,024.30   $1,024.30   $1,024.40