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	$72.40	5.114%	$76.1025	$76.10	$76.10	$76.10
Purchase #2	$220.73	13.185%	$249.8333	$249.83	$249.85	$249.80
Purchase #3	$140.70	4.757%	$147.3931	$147.39	$147.40	$147.40
Purchase #4	$222.69	8.180%	$240.906	$240.91	$240.90	$240.90
Purchase #5	$106.69	4.442%	$111.4292	$111.43	$111.45	$111.40
Purchase #6	$6.96	3.520%	$7.205	$7.21	$7.20	$7.20
Purchase #7	$153.42	10.407%	$169.3864	$169.39	$169.40	$169.40
7 purchase totals =	$923.59		$1,002.2555	$1,002.26	$1,002.30	$1,002.20