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	$154.35	3.562%	$159.8479	$159.85	$159.85	$159.80
Purchase #2	$140.86	12.351%	$158.2576	$158.26	$158.25	$158.30
Purchase #3	$17.82	11.187%	$19.8135	$19.81	$19.80	$19.80
Purchase #4	$123.70	12.473%	$139.1291	$139.13	$139.15	$139.10
Purchase #5	$121.92	11.740%	$136.2334	$136.23	$136.25	$136.20
Purchase #6	$83.73	6.602%	$89.2579	$89.26	$89.25	$89.30
Purchase #7	$86.41	5.476%	$91.1418	$91.14	$91.15	$91.10
7 purchase totals =	$728.79		$793.6812	$793.68	$793.70	$793.60