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 $29.42   10.510%   $32.512   $32.51   $32.50   $32.50  
  Purchase #2 $58.67   13.621%   $66.6614   $66.66   $66.65   $66.70  
  Purchase #3 $212.99   9.361%   $232.928   $232.93   $232.95   $232.90  
  Purchase #4 $56.26   12.530%   $63.3094   $63.31   $63.30   $63.30  
  Purchase #5 $247.68   8.106%   $267.7569   $267.76   $267.75   $267.80  
  Purchase #6 $229.85   7.798%   $247.7737   $247.77   $247.75   $247.80  
  Purchase #7 $107.75   4.686%   $112.7992   $112.80   $112.80   $112.80  
  7 purchase totals = $942.62       $1,023.7406   $1,023.74   $1,023.70   $1,023.80