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 $239.95   8.408%   $260.125   $260.13   $260.15   $260.10  
  Purchase #2 $243.80   7.522%   $262.1386   $262.14   $262.15   $262.10  
  Purchase #3 $47.63   7.235%   $51.076   $51.08   $51.10   $51.10  
  Purchase #4 $114.64   9.548%   $125.5858   $125.59   $125.60   $125.60  
  Purchase #5 $46.64   3.650%   $48.3424   $48.34   $48.35   $48.30  
  Purchase #6 $203.59   7.666%   $219.1972   $219.20   $219.20   $219.20  
  Purchase #7 $228.91   13.641%   $260.1356   $260.14   $260.15   $260.10  
  7 purchase totals = $1,125.16       $1,226.6006   $1,226.62   $1,226.70   $1,226.50