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	$173.37	7.157%	$185.7781	$185.78	$185.80	$185.80
Purchase #2	$241.48	6.173%	$256.3866	$256.39	$256.40	$256.40
Purchase #3	$53.93	8.447%	$58.4855	$58.49	$58.50	$58.50
Purchase #4	$42.76	5.233%	$44.9976	$45.00	$45.00	$45.00
Purchase #5	$53.77	9.648%	$58.9577	$58.96	$58.95	$59.00
Purchase #6	$173.57	13.284%	$196.627	$196.63	$196.65	$196.60
Purchase #7	$80.77	5.339%	$85.0823	$85.08	$85.10	$85.10
7 purchase totals =	$819.65		$886.3148	$886.33	$886.40	$886.40