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	$104.54	12.227%	$117.3221	$117.32	$117.30	$117.30
Purchase #2	$247.76	10.472%	$273.7054	$273.71	$273.70	$273.70
Purchase #3	$140.31	10.116%	$154.5038	$154.50	$154.50	$154.50
Purchase #4	$222.52	12.642%	$250.651	$250.65	$250.65	$250.70
Purchase #5	$77.42	10.865%	$85.8317	$85.83	$85.85	$85.80
Purchase #6	$136.84	6.137%	$145.2379	$145.24	$145.25	$145.20
Purchase #7	$110.39	11.562%	$123.1533	$123.15	$123.15	$123.20
7 purchase totals =	$1,039.78		$1,150.4052	$1,150.40	$1,150.40	$1,150.40