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	$246.57	11.687%	$275.3866	$275.39	$275.40	$275.40
Purchase #2	$171.69	13.685%	$195.1858	$195.19	$195.20	$195.20
Purchase #3	$76.92	7.700%	$82.8428	$82.84	$82.85	$82.80
Purchase #4	$177.65	6.318%	$188.8739	$188.87	$188.85	$188.90
Purchase #5	$82.41	9.170%	$89.967	$89.97	$89.95	$90.00
Purchase #6	$100.72	5.578%	$106.3382	$106.34	$106.35	$106.30
Purchase #7	$176.29	7.868%	$190.1605	$190.16	$190.15	$190.20
7 purchase totals =	$1,032.25		$1,128.7548	$1,128.76	$1,128.75	$1,128.80