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 $192.41   13.617%   $218.6105   $218.61   $218.60   $218.60  
  Purchase #2 $122.51   3.368%   $126.6361   $126.64   $126.65   $126.60  
  Purchase #3 $139.89   4.453%   $146.1193   $146.12   $146.10   $146.10  
  Purchase #4 $49.47   9.178%   $54.0104   $54.01   $54.00   $54.00  
  Purchase #5 $213.37   8.265%   $231.005   $231.01   $231.00   $231.00  
  Purchase #6 $239.67   9.808%   $263.1768   $263.18   $263.20   $263.20  
  Purchase #7 $224.93   13.222%   $254.6702   $254.67   $254.65   $254.70  
  7 purchase totals = $1,182.25       $1,294.2283   $1,294.24   $1,294.20   $1,294.20