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 $54.63   13.545%   $62.0296   $62.03   $62.05   $62.00  
  Purchase #2 $41.51   5.413%   $43.7569   $43.76   $43.75   $43.80  
  Purchase #3 $51.88   3.457%   $53.6735   $53.67   $53.65   $53.70  
  Purchase #4 $67.79   7.858%   $73.1169   $73.12   $73.10   $73.10  
  Purchase #5 $58.94   7.701%   $63.479   $63.48   $63.50   $63.50  
  Purchase #6 $201.50   13.450%   $228.6018   $228.60   $228.60   $228.60  
  Purchase #7 $62.64   5.439%   $66.047   $66.05   $66.05   $66.00  
  7 purchase totals = $538.89       $590.7047   $590.71   $590.70   $590.70