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 $190.57   6.680%   $203.3001   $203.30   $203.30   $203.30  
  Purchase #2 $187.79   4.403%   $196.0584   $196.06   $196.05   $196.10  
  Purchase #3 $15.77   11.663%   $17.6093   $17.61   $17.60   $17.60  
  Purchase #4 $226.89   11.597%   $253.2024   $253.20   $253.20   $253.20  
  Purchase #5 $59.41   8.852%   $64.669   $64.67   $64.65   $64.70  
  Purchase #6 $133.85   10.476%   $147.8721   $147.87   $147.85   $147.90  
  Purchase #7 $202.49   10.205%   $223.1541   $223.15   $223.15   $223.20  
  7 purchase totals = $1,016.77       $1,105.8654   $1,105.86   $1,105.80   $1,106.00