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 $40.96   9.848%   $44.9937   $44.99   $45.00   $45.00  
  Purchase #2 $118.89   9.698%   $130.42   $130.42   $130.40   $130.40  
  Purchase #3 $142.40   9.861%   $156.4421   $156.44   $156.45   $156.40  
  Purchase #4 $17.47   5.166%   $18.3725   $18.37   $18.35   $18.40  
  Purchase #5 $219.74   5.680%   $232.2212   $232.22   $232.20   $232.20  
  Purchase #6 $131.40   10.782%   $145.5675   $145.57   $145.55   $145.60  
  Purchase #7 $81.71   7.857%   $88.13   $88.13   $88.15   $88.10  
  7 purchase totals = $752.57       $816.1470   $816.14   $816.10   $816.10