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	$73.36	13.158%	$83.0127	$83.01	$83.00	$83.00
Purchase #2	$241.26	12.874%	$272.3198	$272.32	$272.30	$272.30
Purchase #3	$144.39	4.743%	$151.2384	$151.24	$151.25	$151.20
Purchase #4	$238.40	4.240%	$248.5082	$248.51	$248.50	$248.50
Purchase #5	$184.86	13.579%	$209.9621	$209.96	$209.95	$210.00
Purchase #6	$224.35	7.626%	$241.4589	$241.46	$241.45	$241.50
Purchase #7	$40.50	3.850%	$42.0593	$42.06	$42.05	$42.10
7 purchase totals =	$1,147.12		$1,248.5594	$1,248.56	$1,248.50	$1,248.60