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	$173.41	8.740%	$188.566	$188.57	$188.55	$188.60
Purchase #2	$221.33	13.692%	$251.6345	$251.63	$251.65	$251.60
Purchase #3	$174.93	9.665%	$191.837	$191.84	$191.85	$191.80
Purchase #4	$134.96	5.689%	$142.6379	$142.64	$142.65	$142.60
Purchase #5	$156.69	6.768%	$167.2948	$167.29	$167.30	$167.30
Purchase #6	$94.53	9.389%	$103.4054	$103.41	$103.40	$103.40
Purchase #7	$229.58	6.501%	$244.505	$244.51	$244.50	$244.50
7 purchase totals =	$1,185.43		$1,289.8806	$1,289.89	$1,289.90	$1,289.80