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 $229.32   5.483%   $241.8936   $241.89   $241.90   $241.90  
  Purchase #2 $98.90   10.355%   $109.1411   $109.14   $109.15   $109.10  
  Purchase #3 $246.79   4.532%   $257.9745   $257.97   $257.95   $258.00  
  Purchase #4 $138.82   3.744%   $144.0174   $144.02   $144.00   $144.00  
  Purchase #5 $95.43   12.613%   $107.4666   $107.47   $107.45   $107.50  
  Purchase #6 $69.47   6.543%   $74.0154   $74.02   $74.00   $74.00  
  Purchase #7 $70.82   3.239%   $73.1139   $73.11   $73.10   $73.10  
  7 purchase totals = $949.55       $1,007.6225   $1,007.62   $1,007.55   $1,007.60