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 $182.49   11.263%   $203.0438   $203.04   $203.05   $203.00  
  Purchase #2 $163.57   7.431%   $175.7249   $175.72   $175.70   $175.70  
  Purchase #3 $60.39   6.256%   $64.168   $64.17   $64.15   $64.20  
  Purchase #4 $73.40   7.218%   $78.698   $78.70   $78.70   $78.70  
  Purchase #5 $47.60   7.282%   $51.0662   $51.07   $51.05   $51.10  
  Purchase #6 $205.47   13.341%   $232.8818   $232.88   $232.90   $232.90  
  Purchase #7 $85.46   7.222%   $91.6319   $91.63   $91.65   $91.60  
  7 purchase totals = $818.38       $897.2146   $897.21   $897.20   $897.20