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	$150.64	13.587%	$171.1075	$171.11	$171.10	$171.10
Purchase #2	$22.29	4.158%	$23.2168	$23.22	$23.20	$23.20
Purchase #3	$66.25	11.606%	$73.939	$73.94	$73.95	$73.90
Purchase #4	$28.37	9.296%	$31.0073	$31.01	$31.00	$31.00
Purchase #5	$93.71	7.312%	$100.5621	$100.56	$100.55	$100.60
Purchase #6	$216.36	3.223%	$223.3333	$223.33	$223.35	$223.30
Purchase #7	$37.53	7.814%	$40.4626	$40.46	$40.45	$40.50
7 purchase totals =	$615.15		$663.6286	$663.63	$663.60	$663.60