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	$48.69	11.465%	$54.2723	$54.27	$54.25	$54.30
Purchase #2	$22.72	8.810%	$24.7216	$24.72	$24.70	$24.70
Purchase #3	$179.39	8.438%	$194.5269	$194.53	$194.55	$194.50
Purchase #4	$33.45	11.526%	$37.3054	$37.31	$37.30	$37.30
Purchase #5	$77.92	3.828%	$80.9028	$80.90	$80.90	$80.90
Purchase #6	$105.76	13.663%	$120.21	$120.21	$120.20	$120.20
Purchase #7	$178.63	12.472%	$200.9087	$200.91	$200.90	$200.90
7 purchase totals =	$646.56		$712.8477	$712.85	$712.80	$712.80