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	$174.27	7.834%	$187.9223	$187.92	$187.90	$187.90
Purchase #2	$139.36	13.582%	$158.2879	$158.29	$158.30	$158.30
Purchase #3	$85.74	3.621%	$88.8446	$88.84	$88.85	$88.80
Purchase #4	$25.81	10.474%	$28.5133	$28.51	$28.50	$28.50
Purchase #5	$209.90	4.723%	$219.8136	$219.81	$219.80	$219.80
Purchase #6	$78.88	8.554%	$85.6274	$85.63	$85.65	$85.60
Purchase #7	$10.81	4.251%	$11.2695	$11.27	$11.25	$11.30
7 purchase totals =	$724.77		$780.2786	$780.27	$780.25	$780.20