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	$26.54	6.482%	$28.2603	$28.26	$28.25	$28.30
Purchase #2	$18.38	12.252%	$20.6319	$20.63	$20.65	$20.60
Purchase #3	$137.74	10.557%	$152.2812	$152.28	$152.30	$152.30
Purchase #4	$48.49	8.208%	$52.4701	$52.47	$52.45	$52.50
Purchase #5	$102.74	3.424%	$106.2578	$106.26	$106.25	$106.30
Purchase #6	$87.46	3.651%	$90.6532	$90.65	$90.65	$90.70
Purchase #7	$154.82	6.478%	$164.8492	$164.85	$164.85	$164.80
7 purchase totals =	$576.17		$615.4037	$615.40	$615.40	$615.50