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	$238.46	5.194%	$250.8456	$250.85	$250.85	$250.80
Purchase #2	$99.36	12.319%	$111.6002	$111.60	$111.60	$111.60
Purchase #3	$150.60	4.489%	$157.3604	$157.36	$157.35	$157.40
Purchase #4	$87.34	12.675%	$98.4103	$98.41	$98.40	$98.40
Purchase #5	$140.71	4.410%	$146.9153	$146.92	$146.90	$146.90
Purchase #6	$99.89	6.357%	$106.24	$106.24	$106.25	$106.20
Purchase #7	$68.66	4.674%	$71.8692	$71.87	$71.85	$71.90
7 purchase totals =	$885.02		$943.2410	$943.25	$943.20	$943.20