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	$136.36	3.642%	$141.3262	$141.33	$141.35	$141.30
Purchase #2	$160.40	7.644%	$172.661	$172.66	$172.65	$172.70
Purchase #3	$105.34	12.148%	$118.1367	$118.14	$118.15	$118.10
Purchase #4	$80.29	6.470%	$85.4848	$85.48	$85.50	$85.50
Purchase #5	$127.56	9.377%	$139.5213	$139.52	$139.50	$139.50
Purchase #6	$76.45	9.560%	$83.7586	$83.76	$83.75	$83.80
Purchase #7	$125.54	11.351%	$139.79	$139.79	$139.80	$139.80
7 purchase totals =	$811.94		$880.6786	$880.68	$880.70	$880.70