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 $106.99   10.581%   $118.3106   $118.31   $118.30   $118.30  
  Purchase #2 $78.93   10.795%   $87.4505   $87.45   $87.45   $87.50  
  Purchase #3 $236.92   7.600%   $254.9259   $254.93   $254.95   $254.90  
  Purchase #4 $188.48   12.115%   $211.3144   $211.31   $211.30   $211.30  
  Purchase #5 $250.94   3.787%   $260.4431   $260.44   $260.45   $260.40  
  Purchase #6 $22.56   8.220%   $24.4144   $24.41   $24.40   $24.40  
  Purchase #7 $60.75   11.294%   $67.6111   $67.61   $67.60   $67.60  
  7 purchase totals = $945.57       $1,024.4700   $1,024.46   $1,024.45   $1,024.40