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 $159.36   6.257%   $169.3312   $169.33   $169.35   $169.30  
  Purchase #2 $222.69   8.188%   $240.9239   $240.92   $240.90   $240.90  
  Purchase #3 $213.69   6.296%   $227.1439   $227.14   $227.15   $227.10  
  Purchase #4 $95.83   8.578%   $104.0503   $104.05   $104.05   $104.10  
  Purchase #5 $168.89   12.310%   $189.6804   $189.68   $189.70   $189.70  
  Purchase #6 $43.45   6.452%   $46.2534   $46.25   $46.25   $46.30  
  Purchase #7 $204.97   11.745%   $229.0437   $229.04   $229.05   $229.00  
  7 purchase totals = $1,108.88       $1,206.4268   $1,206.41   $1,206.45   $1,206.40