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	$38.51	3.575%	$39.8867	$39.89	$39.90	$39.90
Purchase #2	$183.95	7.340%	$197.4519	$197.45	$197.45	$197.50
Purchase #3	$162.26	10.681%	$179.591	$179.59	$179.60	$179.60
Purchase #4	$82.40	8.408%	$89.3282	$89.33	$89.35	$89.30
Purchase #5	$192.93	13.671%	$219.3055	$219.31	$219.30	$219.30
Purchase #6	$110.69	13.670%	$125.8213	$125.82	$125.80	$125.80
Purchase #7	$39.32	7.630%	$42.3201	$42.32	$42.30	$42.30
7 purchase totals =	$810.06		$893.7047	$893.71	$893.70	$893.70