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	$185.70	9.814%	$203.9246	$203.92	$203.90	$203.90
Purchase #2	$233.65	3.669%	$242.2226	$242.22	$242.20	$242.20
Purchase #3	$48.69	3.373%	$50.3323	$50.33	$50.35	$50.30
Purchase #4	$84.68	6.492%	$90.1774	$90.18	$90.20	$90.20
Purchase #5	$72.43	10.285%	$79.8794	$79.88	$79.90	$79.90
Purchase #6	$205.40	8.694%	$223.2575	$223.26	$223.25	$223.30
Purchase #7	$77.28	10.713%	$85.559	$85.56	$85.55	$85.60
7 purchase totals =	$907.83		$975.3528	$975.35	$975.35	$975.40