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 $63.49   9.402%   $69.4593   $69.46   $69.45   $69.50  
  Purchase #2 $81.63   12.827%   $92.1007   $92.10   $92.10   $92.10  
  Purchase #3 $61.91   4.311%   $64.5789   $64.58   $64.60   $64.60  
  Purchase #4 $156.57   6.804%   $167.223   $167.22   $167.20   $167.20  
  Purchase #5 $87.75   10.143%   $96.6505   $96.65   $96.65   $96.70  
  Purchase #6 $203.55   10.347%   $224.6113   $224.61   $224.60   $224.60  
  Purchase #7 $204.56   9.720%   $224.4432   $224.44   $224.45   $224.40  
  7 purchase totals = $859.46       $939.0669   $939.06   $939.05   $939.10