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 $33.50   8.752%   $36.4319   $36.43   $36.45   $36.40  
  Purchase #2 $96.83   13.121%   $109.5351   $109.54   $109.55   $109.50  
  Purchase #3 $165.94   4.593%   $173.5616   $173.56   $173.55   $173.60  
  Purchase #4 $94.58   3.490%   $97.8808   $97.88   $97.90   $97.90  
  Purchase #5 $16.73   7.308%   $17.9526   $17.95   $17.95   $18.00  
  Purchase #6 $141.52   12.559%   $159.2935   $159.29   $159.30   $159.30  
  Purchase #7 $172.29   9.520%   $188.692   $188.69   $188.70   $188.70  
  7 purchase totals = $721.39       $783.3475   $783.34   $783.40   $783.40