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 $66.39   3.120%   $68.4614   $68.46   $68.45   $68.50  
  Purchase #2 $195.89   8.572%   $212.6817   $212.68   $212.70   $212.70  
  Purchase #3 $229.75   12.656%   $258.8272   $258.83   $258.85   $258.80  
  Purchase #4 $152.77   8.398%   $165.5996   $165.60   $165.60   $165.60  
  Purchase #5 $69.77   9.109%   $76.1253   $76.13   $76.15   $76.10  
  Purchase #6 $170.61   10.545%   $188.6008   $188.60   $188.60   $188.60  
  Purchase #7 $77.26   10.674%   $85.5067   $85.51   $85.50   $85.50  
  7 purchase totals = $962.44       $1,055.8027   $1,055.81   $1,055.85   $1,055.80