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 $183.48   4.289%   $191.3495   $191.35   $191.35   $191.30  
  Purchase #2 $158.61   9.684%   $173.9698   $173.97   $173.95   $174.00  
  Purchase #3 $214.55   12.144%   $240.605   $240.61   $240.60   $240.60  
  Purchase #4 $159.71   10.502%   $176.4827   $176.48   $176.50   $176.50  
  Purchase #5 $64.89   6.690%   $69.2311   $69.23   $69.25   $69.20  
  Purchase #6 $22.70   10.185%   $25.012   $25.01   $25.00   $25.00  
  Purchase #7 $69.50   8.204%   $75.2018   $75.20   $75.20   $75.20  
  7 purchase totals = $873.44       $951.8519   $951.85   $951.85   $951.80