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 $56.33   10.216%   $62.0847   $62.08   $62.10   $62.10  
  Purchase #2 $43.48   12.858%   $49.0707   $49.07   $49.05   $49.10  
  Purchase #3 $22.63   5.867%   $23.9577   $23.96   $23.95   $24.00  
  Purchase #4 $69.34   6.368%   $73.7556   $73.76   $73.75   $73.80  
  Purchase #5 $78.55   8.162%   $84.9613   $84.96   $84.95   $85.00  
  Purchase #6 $88.46   4.116%   $92.101   $92.10   $92.10   $92.10  
  Purchase #7 $228.41   8.217%   $247.1784   $247.18   $247.20   $247.20  
  7 purchase totals = $587.20       $633.1094   $633.11   $633.10   $633.30