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 $56.90   8.856%   $61.9391   $61.94   $61.95   $61.90  
  Purchase #2 $80.69   8.610%   $87.6374   $87.64   $87.65   $87.60  
  Purchase #3 $67.38   12.804%   $76.0073   $76.01   $76.00   $76.00  
  Purchase #4 $232.94   10.512%   $257.4267   $257.43   $257.45   $257.40  
  Purchase #5 $87.74   4.227%   $91.4488   $91.45   $91.45   $91.40  
  Purchase #6 $65.55   4.333%   $68.3903   $68.39   $68.40   $68.40  
  Purchase #7 $96.73   12.530%   $108.8503   $108.85   $108.85   $108.90  
  7 purchase totals = $687.93       $751.6999   $751.71   $751.75   $751.60