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 $113.86   5.622%   $120.2612   $120.26   $120.25   $120.30  
  Purchase #2 $190.48   11.847%   $213.0462   $213.05   $213.05   $213.00  
  Purchase #3 $226.93   7.520%   $243.9951   $244.00   $244.00   $244.00  
  Purchase #4 $81.67   6.755%   $87.1868   $87.19   $87.20   $87.20  
  Purchase #5 $244.53   9.455%   $267.6503   $267.65   $267.65   $267.70  
  Purchase #6 $172.73   11.708%   $192.9532   $192.95   $192.95   $193.00  
  Purchase #7 $75.72   8.169%   $81.9056   $81.91   $81.90   $81.90  
  7 purchase totals = $1,105.92       $1,206.9984   $1,207.01   $1,207.00   $1,207.10