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	$121.73	7.804%	$131.2298	$131.23	$131.25	$131.20
Purchase #2	$241.57	12.261%	$271.1889	$271.19	$271.20	$271.20
Purchase #3	$211.54	9.289%	$231.19	$231.19	$231.20	$231.20
Purchase #4	$110.31	11.568%	$123.0707	$123.07	$123.05	$123.10
Purchase #5	$185.89	13.304%	$210.6208	$210.62	$210.60	$210.60
Purchase #6	$18.57	6.690%	$19.8123	$19.81	$19.80	$19.80
Purchase #7	$161.32	10.592%	$178.407	$178.41	$178.40	$178.40
7 purchase totals =	$1,050.93		$1,165.5195	$1,165.52	$1,165.50	$1,165.50