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	$155.89	12.290%	$175.0489	$175.05	$175.05	$175.00
Purchase #2	$88.95	11.653%	$99.3153	$99.32	$99.30	$99.30
Purchase #3	$210.29	8.570%	$228.3119	$228.31	$228.30	$228.30
Purchase #4	$142.40	11.651%	$158.991	$158.99	$159.00	$159.00
Purchase #5	$68.53	4.766%	$71.7961	$71.80	$71.80	$71.80
Purchase #6	$42.47	8.109%	$45.9139	$45.91	$45.90	$45.90
Purchase #7	$156.45	3.488%	$161.907	$161.91	$161.90	$161.90
7 purchase totals =	$864.98		$941.2841	$941.29	$941.25	$941.20