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 $241.48   13.446%   $273.9494   $273.95   $273.95   $273.90  
  Purchase #2 $92.31   6.293%   $98.1191   $98.12   $98.10   $98.10  
  Purchase #3 $111.37   7.718%   $119.9655   $119.97   $119.95   $120.00  
  Purchase #4 $65.27   4.246%   $68.0414   $68.04   $68.05   $68.00  
  Purchase #5 $128.47   11.149%   $142.7931   $142.79   $142.80   $142.80  
  Purchase #6 $206.93   5.787%   $218.905   $218.91   $218.90   $218.90  
  Purchase #7 $30.49   5.689%   $32.2246   $32.22   $32.20   $32.20  
  7 purchase totals = $876.32       $953.9981   $954.00   $953.95   $953.90