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 $154.55   9.792%   $169.6835   $169.68   $169.70   $169.70  
  Purchase #2 $76.27   3.667%   $79.0668   $79.07   $79.05   $79.10  
  Purchase #3 $180.83   11.141%   $200.9763   $200.98   $201.00   $201.00  
  Purchase #4 $59.91   6.860%   $64.0198   $64.02   $64.00   $64.00  
  Purchase #5 $98.41   9.582%   $107.8396   $107.84   $107.85   $107.80  
  Purchase #6 $137.66   3.469%   $142.4354   $142.44   $142.45   $142.40  
  Purchase #7 $174.92   8.147%   $189.1707   $189.17   $189.15   $189.20  
  7 purchase totals = $882.55       $953.1921   $953.20   $953.20   $953.20