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 $207.58   8.414%   $225.0458   $225.05   $225.05   $225.00  
  Purchase #2 $22.70   4.392%   $23.697   $23.70   $23.70   $23.70  
  Purchase #3 $225.89   5.383%   $238.0497   $238.05   $238.05   $238.00  
  Purchase #4 $193.81   11.295%   $215.7008   $215.70   $215.70   $215.70  
  Purchase #5 $40.29   9.242%   $44.0136   $44.01   $44.00   $44.00  
  Purchase #6 $200.88   5.572%   $212.073   $212.07   $212.05   $212.10  
  Purchase #7 $41.28   10.389%   $45.5686   $45.57   $45.55   $45.60  
  7 purchase totals = $932.43       $1,004.1485   $1,004.15   $1,004.10   $1,004.10