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	$235.32	3.357%	$243.2197	$243.22	$243.20	$243.20
Purchase #2	$42.76	4.596%	$44.7252	$44.73	$44.75	$44.70
Purchase #3	$148.77	7.834%	$160.4246	$160.42	$160.40	$160.40
Purchase #4	$177.67	3.227%	$183.4034	$183.40	$183.40	$183.40
Purchase #5	$83.58	7.609%	$89.9396	$89.94	$89.95	$89.90
Purchase #6	$39.61	7.405%	$42.5431	$42.54	$42.55	$42.50
Purchase #7	$37.91	13.130%	$42.8876	$42.89	$42.90	$42.90
7 purchase totals =	$765.62		$807.1432	$807.14	$807.15	$807.00