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	$236.76	7.589%	$254.7277	$254.73	$254.75	$254.70
Purchase #2	$94.89	10.488%	$104.8421	$104.84	$104.85	$104.80
Purchase #3	$142.72	8.681%	$155.1095	$155.11	$155.10	$155.10
Purchase #4	$121.40	5.405%	$127.9617	$127.96	$127.95	$128.00
Purchase #5	$35.69	4.668%	$37.356	$37.36	$37.35	$37.40
Purchase #6	$94.61	3.451%	$97.875	$97.88	$97.90	$97.90
Purchase #7	$156.68	3.743%	$162.5445	$162.54	$162.55	$162.50
7 purchase totals =	$882.75		$940.4165	$940.42	$940.45	$940.40