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	$146.46	13.267%	$165.8908	$165.89	$165.90	$165.90
Purchase #2	$52.42	13.775%	$59.6409	$59.64	$59.65	$59.60
Purchase #3	$120.60	6.332%	$128.2364	$128.24	$128.25	$128.20
Purchase #4	$234.59	6.736%	$250.392	$250.39	$250.40	$250.40
Purchase #5	$22.64	3.142%	$23.3513	$23.35	$23.35	$23.40
Purchase #6	$159.34	11.868%	$178.2505	$178.25	$178.25	$178.30
Purchase #7	$110.91	7.399%	$119.1162	$119.12	$119.10	$119.10
7 purchase totals =	$846.96		$924.8781	$924.88	$924.90	$924.90