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 $225.97   7.364%   $242.6104   $242.61   $242.60   $242.60  
  Purchase #2 $212.61   12.407%   $238.9885   $238.99   $239.00   $239.00  
  Purchase #3 $216.43   8.488%   $234.8006   $234.80   $234.80   $234.80  
  Purchase #4 $201.90   7.438%   $216.9173   $216.92   $216.90   $216.90  
  Purchase #5 $120.63   10.427%   $133.2081   $133.21   $133.20   $133.20  
  Purchase #6 $168.97   4.519%   $176.6058   $176.61   $176.60   $176.60  
  Purchase #7 $207.65   12.638%   $233.8928   $233.89   $233.90   $233.90  
  7 purchase totals = $1,354.16       $1,477.0235   $1,477.03   $1,477.00   $1,477.00