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 $183.33   3.317%   $189.4111   $189.41   $189.40   $189.40  
  Purchase #2 $116.38   4.187%   $121.2528   $121.25   $121.25   $121.30  
  Purchase #3 $170.65   6.807%   $182.2661   $182.27   $182.25   $182.30  
  Purchase #4 $190.38   9.734%   $208.9116   $208.91   $208.90   $208.90  
  Purchase #5 $140.39   6.469%   $149.4718   $149.47   $149.45   $149.50  
  Purchase #6 $106.59   13.652%   $121.1417   $121.14   $121.15   $121.10  
  Purchase #7 $128.82   6.331%   $136.9756   $136.98   $137.00   $137.00  
  7 purchase totals = $1,036.54       $1,109.4307   $1,109.43   $1,109.40   $1,109.50