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 $54.48   12.683%   $61.3897   $61.39   $61.40   $61.40  
  Purchase #2 $84.82   12.367%   $95.3097   $95.31   $95.30   $95.30  
  Purchase #3 $56.70   3.255%   $58.5456   $58.55   $58.55   $58.50  
  Purchase #4 $95.92   8.492%   $104.0655   $104.07   $104.05   $104.10  
  Purchase #5 $181.35   5.738%   $191.7559   $191.76   $191.75   $191.80  
  Purchase #6 $104.47   13.109%   $118.165   $118.17   $118.15   $118.20  
  Purchase #7 $66.73   6.702%   $71.2022   $71.20   $71.20   $71.20  
  7 purchase totals = $644.47       $700.4336   $700.45   $700.40   $700.50