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 $244.27   7.642%   $262.9371   $262.94   $262.95   $262.90  
  Purchase #2 $163.30   10.846%   $181.0115   $181.01   $181.00   $181.00  
  Purchase #3 $48.72   10.595%   $53.8819   $53.88   $53.90   $53.90  
  Purchase #4 $99.76   7.620%   $107.3617   $107.36   $107.35   $107.40  
  Purchase #5 $125.70   12.761%   $141.7406   $141.74   $141.75   $141.70  
  Purchase #6 $226.94   10.179%   $250.0402   $250.04   $250.05   $250.00  
  Purchase #7 $112.40   12.482%   $126.4298   $126.43   $126.45   $126.40  
  7 purchase totals = $1,021.09       $1,123.4028   $1,123.40   $1,123.45   $1,123.30