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 $242.95   10.204%   $267.7406   $267.74   $267.75   $267.70  
  Purchase #2 $146.96   13.459%   $166.7393   $166.74   $166.75   $166.70  
  Purchase #3 $244.89   9.518%   $268.1986   $268.20   $268.20   $268.20  
  Purchase #4 $104.76   11.464%   $116.7697   $116.77   $116.75   $116.80  
  Purchase #5 $20.29   9.370%   $22.1912   $22.19   $22.20   $22.20  
  Purchase #6 $217.44   12.274%   $244.1286   $244.13   $244.15   $244.10  
  Purchase #7 $114.57   7.388%   $123.0344   $123.03   $123.05   $123.00  
  7 purchase totals = $1,091.86       $1,208.8024   $1,208.80   $1,208.85   $1,208.70