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	$113.66	6.152%	$120.6524	$120.65	$120.65	$120.70
Purchase #2	$247.42	10.419%	$273.1987	$273.20	$273.20	$273.20
Purchase #3	$18.70	5.730%	$19.7715	$19.77	$19.75	$19.80
Purchase #4	$139.82	9.122%	$152.5744	$152.57	$152.55	$152.60
Purchase #5	$28.50	12.708%	$32.1218	$32.12	$32.10	$32.10
Purchase #6	$85.71	4.296%	$89.3921	$89.39	$89.40	$89.40
Purchase #7	$103.50	6.122%	$109.8363	$109.84	$109.85	$109.80
7 purchase totals =	$737.31		$797.5472	$797.54	$797.50	$797.60