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	$17.82	3.851%	$18.5062	$18.51	$18.50	$18.50
Purchase #2	$129.64	5.228%	$136.4176	$136.42	$136.40	$136.40
Purchase #3	$43.79	12.729%	$49.364	$49.36	$49.35	$49.40
Purchase #4	$58.74	6.854%	$62.766	$62.77	$62.75	$62.80
Purchase #5	$245.71	3.732%	$254.8799	$254.88	$254.90	$254.90
Purchase #6	$72.75	13.352%	$82.4636	$82.46	$82.45	$82.50
Purchase #7	$152.76	10.472%	$168.757	$168.76	$168.75	$168.80
7 purchase totals =	$721.21		$773.1543	$773.16	$773.10	$773.30