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 $247.72   8.568%   $268.9446   $268.94   $268.95   $268.90  
  Purchase #2 $31.42   13.137%   $35.5476   $35.55   $35.55   $35.50  
  Purchase #3 $123.49   3.396%   $127.6837   $127.68   $127.70   $127.70  
  Purchase #4 $76.39   10.825%   $84.6592   $84.66   $84.65   $84.70  
  Purchase #5 $146.58   13.798%   $166.8051   $166.81   $166.80   $166.80  
  Purchase #6 $142.84   6.285%   $151.8175   $151.82   $151.80   $151.80  
  Purchase #7 $14.78   13.123%   $16.7196   $16.72   $16.70   $16.70  
  7 purchase totals = $783.22       $852.1773   $852.18   $852.15   $852.10