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	$73.79	6.481%	$78.5723	$78.57	$78.55	$78.60
Purchase #2	$28.77	11.559%	$32.0955	$32.10	$32.10	$32.10
Purchase #3	$55.58	13.162%	$62.8954	$62.90	$62.90	$62.90
Purchase #4	$147.31	12.578%	$165.8387	$165.84	$165.85	$165.80
Purchase #5	$133.88	11.218%	$148.8987	$148.90	$148.90	$148.90
Purchase #6	$16.28	11.213%	$18.1055	$18.11	$18.10	$18.10
Purchase #7	$173.87	4.279%	$181.3099	$181.31	$181.30	$181.30
7 purchase totals =	$629.48		$687.7160	$687.73	$687.70	$687.70