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	$142.59	10.828%	$158.0296	$158.03	$158.05	$158.00
Purchase #2	$223.56	11.293%	$248.8066	$248.81	$248.80	$248.80
Purchase #3	$69.33	4.198%	$72.2405	$72.24	$72.25	$72.20
Purchase #4	$59.55	5.263%	$62.6841	$62.68	$62.70	$62.70
Purchase #5	$39.35	5.181%	$41.3887	$41.39	$41.40	$41.40
Purchase #6	$247.77	7.310%	$265.882	$265.88	$265.90	$265.90
Purchase #7	$221.88	4.164%	$231.1191	$231.12	$231.10	$231.10
7 purchase totals =	$1,004.03		$1,080.1506	$1,080.15	$1,080.20	$1,080.10