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	$102.47	3.811%	$106.3751	$106.38	$106.40	$106.40
Purchase #2	$47.28	8.209%	$51.1612	$51.16	$51.15	$51.20
Purchase #3	$28.53	3.404%	$29.5012	$29.50	$29.50	$29.50
Purchase #4	$36.84	13.668%	$41.8753	$41.88	$41.90	$41.90
Purchase #5	$149.68	8.532%	$162.4507	$162.45	$162.45	$162.50
Purchase #6	$18.42	11.258%	$20.4937	$20.49	$20.50	$20.50
Purchase #7	$247.94	13.700%	$281.9078	$281.91	$281.90	$281.90
7 purchase totals =	$631.16		$693.7650	$693.77	$693.80	$693.90