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	$150.79	3.236%	$155.6696	$155.67	$155.65	$155.70
Purchase #2	$57.51	6.459%	$61.2246	$61.22	$61.20	$61.20
Purchase #3	$115.95	12.774%	$130.7615	$130.76	$130.75	$130.80
Purchase #4	$81.41	9.742%	$89.341	$89.34	$89.35	$89.30
Purchase #5	$79.92	12.198%	$89.6686	$89.67	$89.65	$89.70
Purchase #6	$240.93	4.275%	$251.2298	$251.23	$251.25	$251.20
Purchase #7	$206.49	8.678%	$224.4092	$224.41	$224.40	$224.40
7 purchase totals =	$933.00		$1,002.3043	$1,002.30	$1,002.25	$1,002.30