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 $246.70   6.220%   $262.0447   $262.04   $262.05   $262.00  
  Purchase #2 $195.71   4.627%   $204.7655   $204.77   $204.75   $204.80  
  Purchase #3 $47.81   9.187%   $52.2023   $52.20   $52.20   $52.20  
  Purchase #4 $248.35   7.528%   $267.0458   $267.05   $267.05   $267.00  
  Purchase #5 $232.29   12.699%   $261.7885   $261.79   $261.80   $261.80  
  Purchase #6 $116.98   7.714%   $126.0038   $126.00   $126.00   $126.00  
  Purchase #7 $110.60   13.280%   $125.2877   $125.29   $125.30   $125.30  
  7 purchase totals = $1,198.44       $1,299.1383   $1,299.14   $1,299.15   $1,299.10