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 $41.97   6.180%   $44.5637   $44.56   $44.55   $44.60  
  Purchase #2 $167.32   11.172%   $186.013   $186.01   $186.00   $186.00  
  Purchase #3 $52.64   9.666%   $57.7282   $57.73   $57.75   $57.70  
  Purchase #4 $182.62   10.639%   $202.0489   $202.05   $202.05   $202.00  
  Purchase #5 $113.26   4.247%   $118.0702   $118.07   $118.05   $118.10  
  Purchase #6 $39.88   12.614%   $44.9105   $44.91   $44.90   $44.90  
  Purchase #7 $106.42   5.769%   $112.5594   $112.56   $112.55   $112.60  
  7 purchase totals = $704.11       $765.8939   $765.89   $765.85   $765.90