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	$167.93	12.755%	$189.3495	$189.35	$189.35	$189.30
Purchase #2	$106.40	12.766%	$119.983	$119.98	$120.00	$120.00
Purchase #3	$66.83	7.229%	$71.6611	$71.66	$71.65	$71.70
Purchase #4	$133.83	12.465%	$150.5119	$150.51	$150.50	$150.50
Purchase #5	$201.32	11.158%	$223.7833	$223.78	$223.80	$223.80
Purchase #6	$10.38	10.538%	$11.4738	$11.47	$11.45	$11.50
Purchase #7	$12.59	13.731%	$14.3187	$14.32	$14.30	$14.30
7 purchase totals =	$699.28		$781.0813	$781.07	$781.05	$781.10