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 $25.50   11.435%   $28.4159   $28.42   $28.40   $28.40  
  Purchase #2 $67.70   3.534%   $70.0925   $70.09   $70.10   $70.10  
  Purchase #3 $168.38   3.839%   $174.8441   $174.84   $174.85   $174.80  
  Purchase #4 $144.44   3.471%   $149.4535   $149.45   $149.45   $149.50  
  Purchase #5 $100.88   9.750%   $110.7158   $110.72   $110.70   $110.70  
  Purchase #6 $103.79   5.238%   $109.2265   $109.23   $109.25   $109.20  
  Purchase #7 $57.82   6.171%   $61.3881   $61.39   $61.40   $61.40  
  7 purchase totals = $668.51       $704.1364   $704.14   $704.15   $704.10