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 $52.98   4.848%   $55.5485   $55.55   $55.55   $55.50  
  Purchase #2 $200.49   7.213%   $214.9513   $214.95   $214.95   $215.00  
  Purchase #3 $103.29   8.487%   $112.0562   $112.06   $112.05   $112.10  
  Purchase #4 $235.40   4.737%   $246.5509   $246.55   $246.55   $246.60  
  Purchase #5 $232.95   12.355%   $261.731   $261.73   $261.75   $261.70  
  Purchase #6 $91.40   9.763%   $100.3234   $100.32   $100.30   $100.30  
  Purchase #7 $21.92   4.765%   $22.9645   $22.96   $22.95   $23.00  
  7 purchase totals = $938.43       $1,014.1258   $1,014.12   $1,014.10   $1,014.20