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 $242.61   8.474%   $263.1688   $263.17   $263.15   $263.20  
  Purchase #2 $25.63   13.784%   $29.1628   $29.16   $29.15   $29.20  
  Purchase #3 $106.47   13.261%   $120.589   $120.59   $120.60   $120.60  
  Purchase #4 $125.86   7.417%   $135.195   $135.20   $135.20   $135.20  
  Purchase #5 $57.56   4.190%   $59.9718   $59.97   $59.95   $60.00  
  Purchase #6 $233.45   7.108%   $250.0436   $250.04   $250.05   $250.00  
  Purchase #7 $192.68   3.367%   $199.1675   $199.17   $199.15   $199.20  
  7 purchase totals = $984.26       $1,057.2985   $1,057.30   $1,057.25   $1,057.40