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 $203.89   13.316%   $231.04   $231.04   $231.05   $231.00  
  Purchase #2 $203.60   6.195%   $216.213   $216.21   $216.20   $216.20  
  Purchase #3 $197.99   8.174%   $214.1737   $214.17   $214.15   $214.20  
  Purchase #4 $236.39   5.613%   $249.6586   $249.66   $249.65   $249.70  
  Purchase #5 $143.68   11.628%   $160.3871   $160.39   $160.40   $160.40  
  Purchase #6 $73.66   9.162%   $80.4087   $80.41   $80.40   $80.40  
  Purchase #7 $66.92   11.460%   $74.589   $74.59   $74.60   $74.60  
  7 purchase totals = $1,126.13       $1,226.4701   $1,226.47   $1,226.45   $1,226.50