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	$136.67	9.214%	$149.2628	$149.26	$149.25	$149.30
Purchase #2	$168.58	3.288%	$174.1229	$174.12	$174.10	$174.10
Purchase #3	$237.39	11.281%	$264.17	$264.17	$264.15	$264.20
Purchase #4	$144.34	4.512%	$150.8526	$150.85	$150.85	$150.90
Purchase #5	$213.28	9.303%	$233.1214	$233.12	$233.10	$233.10
Purchase #6	$68.74	5.346%	$72.4148	$72.41	$72.40	$72.40
Purchase #7	$49.91	13.780%	$56.7876	$56.79	$56.80	$56.80
7 purchase totals =	$1,018.91		$1,100.7321	$1,100.72	$1,100.65	$1,100.80