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 $68.55   6.546%   $73.0373   $73.04   $73.05   $73.00  
  Purchase #2 $115.72   3.329%   $119.5723   $119.57   $119.55   $119.60  
  Purchase #3 $219.46   8.318%   $237.7147   $237.71   $237.70   $237.70  
  Purchase #4 $244.93   10.638%   $270.9857   $270.99   $271.00   $271.00  
  Purchase #5 $130.64   6.183%   $138.7175   $138.72   $138.70   $138.70  
  Purchase #6 $164.99   9.727%   $181.0386   $181.04   $181.05   $181.00  
  Purchase #7 $123.68   13.666%   $140.5821   $140.58   $140.60   $140.60  
  7 purchase totals = $1,067.97       $1,161.6482   $1,161.65   $1,161.65   $1,161.60