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	$72.56	7.780%	$78.2052	$78.21	$78.20	$78.20
Purchase #2	$144.68	3.758%	$150.1171	$150.12	$150.10	$150.10
Purchase #3	$69.58	5.647%	$73.5092	$73.51	$73.50	$73.50
Purchase #4	$60.27	7.499%	$64.7896	$64.79	$64.80	$64.80
Purchase #5	$25.92	10.482%	$28.6369	$28.64	$28.65	$28.60
Purchase #6	$31.33	7.192%	$33.5833	$33.58	$33.60	$33.60
Purchase #7	$163.66	4.231%	$170.5845	$170.58	$170.60	$170.60
7 purchase totals =	$568.00		$599.4258	$599.43	$599.45	$599.40