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	$213.77	12.316%	$240.0979	$240.10	$240.10	$240.10
Purchase #2	$87.62	3.562%	$90.741	$90.74	$90.75	$90.70
Purchase #3	$56.50	4.469%	$59.025	$59.03	$59.05	$59.00
Purchase #4	$128.74	12.313%	$144.5918	$144.59	$144.60	$144.60
Purchase #5	$65.25	11.293%	$72.6187	$72.62	$72.60	$72.60
Purchase #6	$135.74	12.745%	$153.0401	$153.04	$153.05	$153.00
Purchase #7	$107.51	10.864%	$119.1899	$119.19	$119.20	$119.20
7 purchase totals =	$795.13		$879.3044	$879.31	$879.35	$879.20