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 $200.95   11.673%   $224.4069   $224.41   $224.40   $224.40  
  Purchase #2 $78.75   6.203%   $83.6349   $83.63   $83.65   $83.60  
  Purchase #3 $168.79   9.323%   $184.5263   $184.53   $184.55   $184.50  
  Purchase #4 $60.58   5.558%   $63.947   $63.95   $63.95   $63.90  
  Purchase #5 $173.49   3.495%   $179.5535   $179.55   $179.55   $179.60  
  Purchase #6 $128.25   4.736%   $134.3239   $134.32   $134.30   $134.30  
  Purchase #7 $160.26   11.258%   $178.3021   $178.30   $178.30   $178.30  
  7 purchase totals = $971.07       $1,048.6946   $1,048.69   $1,048.70   $1,048.60