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 $233.91   11.524%   $260.8658   $260.87   $260.85   $260.90  
  Purchase #2 $14.91   13.386%   $16.9059   $16.91   $16.90   $16.90  
  Purchase #3 $56.98   5.667%   $60.2091   $60.21   $60.20   $60.20  
  Purchase #4 $182.26   5.768%   $192.7728   $192.77   $192.75   $192.80  
  Purchase #5 $240.51   8.442%   $260.8139   $260.81   $260.80   $260.80  
  Purchase #6 $9.74   7.724%   $10.4923   $10.49   $10.50   $10.50  
  Purchase #7 $237.43   7.341%   $254.8597   $254.86   $254.85   $254.90  
  7 purchase totals = $975.74       $1,056.9195   $1,056.92   $1,056.85   $1,057.00