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	$244.25	6.156%	$259.286	$259.29	$259.30	$259.30
Purchase #2	$111.73	3.430%	$115.5623	$115.56	$115.55	$115.60
Purchase #3	$18.29	8.801%	$19.8997	$19.90	$19.90	$19.90
Purchase #4	$91.79	7.310%	$98.4998	$98.50	$98.50	$98.50
Purchase #5	$87.34	3.529%	$90.4222	$90.42	$90.40	$90.40
Purchase #6	$148.76	13.860%	$169.3781	$169.38	$169.40	$169.40
Purchase #7	$51.41	7.191%	$55.1069	$55.11	$55.10	$55.10
7 purchase totals =	$753.57		$808.1550	$808.16	$808.15	$808.20