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	$52.73	4.809%	$55.2658	$55.27	$55.25	$55.30
Purchase #2	$80.51	4.632%	$84.2392	$84.24	$84.25	$84.20
Purchase #3	$196.74	13.148%	$222.6074	$222.61	$222.60	$222.60
Purchase #4	$137.67	6.728%	$146.9324	$146.93	$146.95	$146.90
Purchase #5	$36.25	11.282%	$40.3397	$40.34	$40.35	$40.30
Purchase #6	$96.97	8.710%	$105.4161	$105.42	$105.40	$105.40
Purchase #7	$84.90	8.805%	$92.3754	$92.38	$92.40	$92.40
7 purchase totals =	$685.77		$747.1760	$747.19	$747.20	$747.10