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	$29.43	10.560%	$32.5378	$32.54	$32.55	$32.50
Purchase #2	$56.54	3.468%	$58.5008	$58.50	$58.50	$58.50
Purchase #3	$141.80	10.367%	$156.5004	$156.50	$156.50	$156.50
Purchase #4	$142.29	9.799%	$156.233	$156.23	$156.25	$156.20
Purchase #5	$228.93	6.840%	$244.5888	$244.59	$244.60	$244.60
Purchase #6	$75.79	8.707%	$82.389	$82.39	$82.40	$82.40
Purchase #7	$155.52	6.490%	$165.6132	$165.61	$165.60	$165.60
7 purchase totals =	$830.30		$896.3630	$896.36	$896.40	$896.30