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 $62.76   9.354%   $68.6306   $68.63   $68.65   $68.60  
  Purchase #2 $72.97   6.834%   $77.9568   $77.96   $77.95   $78.00  
  Purchase #3 $187.82   6.122%   $199.3183   $199.32   $199.30   $199.30  
  Purchase #4 $68.65   5.129%   $72.1711   $72.17   $72.15   $72.20  
  Purchase #5 $162.34   12.873%   $183.238   $183.24   $183.25   $183.20  
  Purchase #6 $226.79   11.816%   $253.5875   $253.59   $253.60   $253.60  
  Purchase #7 $26.63   10.122%   $29.3255   $29.33   $29.35   $29.30  
  7 purchase totals = $807.96       $884.2278   $884.24   $884.25   $884.20