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	$80.48	13.711%	$91.5146	$91.51	$91.50	$91.50
Purchase #2	$15.28	3.826%	$15.8646	$15.86	$15.85	$15.90
Purchase #3	$121.63	5.180%	$127.9304	$127.93	$127.95	$127.90
Purchase #4	$198.47	5.413%	$209.2132	$209.21	$209.20	$209.20
Purchase #5	$25.51	12.702%	$28.7503	$28.75	$28.75	$28.80
Purchase #6	$90.51	11.772%	$101.1648	$101.16	$101.15	$101.20
Purchase #7	$242.62	11.637%	$270.8537	$270.85	$270.85	$270.90
7 purchase totals =	$774.50		$845.2916	$845.27	$845.25	$845.40