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 $203.58   8.817%   $221.5296   $221.53   $221.55   $221.50  
  Purchase #2 $171.57   10.127%   $188.9449   $188.94   $188.95   $188.90  
  Purchase #3 $19.62   10.511%   $21.6823   $21.68   $21.70   $21.70  
  Purchase #4 $159.48   4.209%   $166.1925   $166.19   $166.20   $166.20  
  Purchase #5 $142.31   10.423%   $157.143   $157.14   $157.15   $157.10  
  Purchase #6 $216.75   12.844%   $244.5894   $244.59   $244.60   $244.60  
  Purchase #7 $246.83   8.187%   $267.038   $267.04   $267.05   $267.00  
  7 purchase totals = $1,160.14       $1,267.1197   $1,267.11   $1,267.20   $1,267.00