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 $217.58   8.147%   $235.3062   $235.31   $235.30   $235.30  
  Purchase #2 $125.97   9.575%   $138.0316   $138.03   $138.05   $138.00  
  Purchase #3 $205.99   10.394%   $227.4006   $227.40   $227.40   $227.40  
  Purchase #4 $65.74   4.587%   $68.7555   $68.76   $68.75   $68.80  
  Purchase #5 $164.95   9.555%   $180.711   $180.71   $180.70   $180.70  
  Purchase #6 $166.30   5.129%   $174.8295   $174.83   $174.85   $174.80  
  Purchase #7 $221.99   7.208%   $237.991   $237.99   $238.00   $238.00  
  7 purchase totals = $1,168.52       $1,263.0254   $1,263.03   $1,263.05   $1,263.00