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 $156.89   8.553%   $170.3088   $170.31   $170.30   $170.30  
  Purchase #2 $101.96   4.380%   $106.4258   $106.43   $106.45   $106.40  
  Purchase #3 $33.60   8.582%   $36.4836   $36.48   $36.50   $36.50  
  Purchase #4 $72.41   5.835%   $76.6351   $76.64   $76.65   $76.60  
  Purchase #5 $84.40   3.319%   $87.2012   $87.20   $87.20   $87.20  
  Purchase #6 $26.26   6.539%   $27.9771   $27.98   $28.00   $28.00  
  Purchase #7 $250.85   7.769%   $270.3385   $270.34   $270.35   $270.30  
  7 purchase totals = $726.37       $775.3701   $775.38   $775.45   $775.30