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	$158.36	8.544%	$171.8903	$171.89	$171.90	$171.90
Purchase #2	$87.62	12.723%	$98.7679	$98.77	$98.75	$98.80
Purchase #3	$38.49	13.180%	$43.563	$43.56	$43.55	$43.60
Purchase #4	$154.30	12.448%	$173.5073	$173.51	$173.50	$173.50
Purchase #5	$82.84	10.608%	$91.6277	$91.63	$91.65	$91.60
Purchase #6	$155.75	6.150%	$165.3286	$165.33	$165.35	$165.30
Purchase #7	$193.73	6.242%	$205.8226	$205.82	$205.80	$205.80
7 purchase totals =	$871.09		$950.5074	$950.51	$950.50	$950.50