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 $241.50   5.307%   $254.3164   $254.32   $254.30   $254.30  
  Purchase #2 $244.28   6.238%   $259.5182   $259.52   $259.50   $259.50  
  Purchase #3 $55.44   9.693%   $60.8138   $60.81   $60.80   $60.80  
  Purchase #4 $216.28   4.814%   $226.6917   $226.69   $226.70   $226.70  
  Purchase #5 $235.47   10.592%   $260.411   $260.41   $260.40   $260.40  
  Purchase #6 $56.77   3.464%   $58.7365   $58.74   $58.75   $58.70  
  Purchase #7 $217.74   6.247%   $231.3422   $231.34   $231.35   $231.30  
  7 purchase totals = $1,267.48       $1,351.8298   $1,351.83   $1,351.80   $1,351.70