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 $215.32   12.824%   $242.9326   $242.93   $242.95   $242.90  
  Purchase #2 $240.98   10.687%   $266.7335   $266.73   $266.75   $266.70  
  Purchase #3 $198.36   9.722%   $217.6446   $217.64   $217.65   $217.60  
  Purchase #4 $104.47   13.542%   $118.6173   $118.62   $118.60   $118.60  
  Purchase #5 $119.88   13.546%   $136.1189   $136.12   $136.10   $136.10  
  Purchase #6 $51.70   11.454%   $57.6217   $57.62   $57.60   $57.60  
  Purchase #7 $217.64   11.704%   $243.1126   $243.11   $243.10   $243.10  
  7 purchase totals = $1,148.35       $1,282.7812   $1,282.77   $1,282.75   $1,282.60