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 $59.85   10.821%   $66.3264   $66.33   $66.35   $66.30  
  Purchase #2 $115.80   9.826%   $127.1785   $127.18   $127.20   $127.20  
  Purchase #3 $232.59   9.247%   $254.0976   $254.10   $254.10   $254.10  
  Purchase #4 $248.65   6.483%   $264.77   $264.77   $264.75   $264.80  
  Purchase #5 $182.39   8.127%   $197.2128   $197.21   $197.20   $197.20  
  Purchase #6 $124.81   8.693%   $135.6597   $135.66   $135.65   $135.70  
  Purchase #7 $18.90   9.773%   $20.7471   $20.75   $20.75   $20.70  
  7 purchase totals = $982.99       $1,065.9921   $1,066.00   $1,066.00   $1,066.00