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	$141.89	5.788%	$150.1026	$150.10	$150.10	$150.10
Purchase #2	$139.86	7.113%	$149.8082	$149.81	$149.80	$149.80
Purchase #3	$127.30	13.122%	$144.0043	$144.00	$144.00	$144.00
Purchase #4	$155.95	7.498%	$167.6431	$167.64	$167.65	$167.60
Purchase #5	$17.56	6.720%	$18.74	$18.74	$18.75	$18.70
Purchase #6	$18.75	7.635%	$20.1816	$20.18	$20.20	$20.20
Purchase #7	$37.56	13.274%	$42.5457	$42.55	$42.55	$42.50
7 purchase totals =	$638.87		$693.0255	$693.02	$693.05	$692.90