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 $242.49   10.754%   $268.5674   $268.57   $268.55   $268.60  
  Purchase #2 $163.82   7.435%   $176   $176.00   $176.00   $176.00  
  Purchase #3 $115.55   7.563%   $124.289   $124.29   $124.30   $124.30  
  Purchase #4 $64.36   11.120%   $71.5168   $71.52   $71.50   $71.50  
  Purchase #5 $215.57   11.661%   $240.7076   $240.71   $240.70   $240.70  
  Purchase #6 $67.88   11.867%   $75.9353   $75.94   $75.95   $75.90  
  Purchase #7 $22.82   6.247%   $24.2456   $24.25   $24.25   $24.20  
  7 purchase totals = $892.49       $981.2617   $981.28   $981.25   $981.20