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 $58.43   13.820%   $66.505   $66.51   $66.50   $66.50  
  Purchase #2 $159.34   9.363%   $174.259   $174.26   $174.25   $174.30  
  Purchase #3 $181.89   12.652%   $204.9027   $204.90   $204.90   $204.90  
  Purchase #4 $32.57   10.725%   $36.0631   $36.06   $36.05   $36.10  
  Purchase #5 $100.89   9.258%   $110.2304   $110.23   $110.25   $110.20  
  Purchase #6 $174.90   6.868%   $186.9121   $186.91   $186.90   $186.90  
  Purchase #7 $169.78   5.810%   $179.6442   $179.64   $179.65   $179.60  
  7 purchase totals = $877.80       $958.5165   $958.51   $958.50   $958.50