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 $195.62   6.324%   $207.991   $207.99   $208.00   $208.00  
  Purchase #2 $28.27   8.541%   $30.6845   $30.68   $30.70   $30.70  
  Purchase #3 $51.93   7.799%   $55.98   $55.98   $56.00   $56.00  
  Purchase #4 $219.26   11.350%   $244.146   $244.15   $244.15   $244.10  
  Purchase #5 $165.60   9.762%   $181.7659   $181.77   $181.75   $181.80  
  Purchase #6 $59.90   9.189%   $65.4042   $65.40   $65.40   $65.40  
  Purchase #7 $26.59   10.867%   $29.4795   $29.48   $29.50   $29.50  
  7 purchase totals = $747.17       $815.4511   $815.45   $815.50   $815.50