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	$109.94	6.667%	$117.2697	$117.27	$117.25	$117.30
Purchase #2	$81.39	7.804%	$87.7417	$87.74	$87.75	$87.70
Purchase #3	$237.46	7.767%	$255.9035	$255.90	$255.90	$255.90
Purchase #4	$18.45	12.506%	$20.7574	$20.76	$20.75	$20.80
Purchase #5	$140.99	8.161%	$152.4962	$152.50	$152.50	$152.50
Purchase #6	$143.52	6.543%	$152.9105	$152.91	$152.90	$152.90
Purchase #7	$94.85	6.601%	$101.111	$101.11	$101.10	$101.10
7 purchase totals =	$826.60		$888.1900	$888.19	$888.15	$888.20