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	$65.83	8.476%	$71.4098	$71.41	$71.40	$71.40
Purchase #2	$30.47	8.796%	$33.1501	$33.15	$33.15	$33.20
Purchase #3	$143.42	9.169%	$156.5702	$156.57	$156.55	$156.60
Purchase #4	$52.87	7.590%	$56.8828	$56.88	$56.90	$56.90
Purchase #5	$152.27	4.354%	$158.8998	$158.90	$158.90	$158.90
Purchase #6	$140.82	7.334%	$151.1477	$151.15	$151.15	$151.10
Purchase #7	$203.73	4.608%	$213.1179	$213.12	$213.10	$213.10
7 purchase totals =	$789.41		$841.1783	$841.18	$841.15	$841.20