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	$193.49	9.803%	$212.4578	$212.46	$212.45	$212.50
Purchase #2	$39.68	6.438%	$42.2346	$42.23	$42.25	$42.20
Purchase #3	$140.69	8.522%	$152.6796	$152.68	$152.70	$152.70
Purchase #4	$130.40	11.128%	$144.9109	$144.91	$144.90	$144.90
Purchase #5	$39.89	13.376%	$45.2257	$45.23	$45.25	$45.20
Purchase #6	$153.97	3.835%	$159.8747	$159.87	$159.85	$159.90
Purchase #7	$91.42	7.609%	$98.3761	$98.38	$98.40	$98.40
7 purchase totals =	$789.54		$855.7594	$855.76	$855.80	$855.80