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	$42.47	7.815%	$45.789	$45.79	$45.80	$45.80
Purchase #2	$25.37	7.403%	$27.2481	$27.25	$27.25	$27.20
Purchase #3	$242.71	3.208%	$250.4961	$250.50	$250.50	$250.50
Purchase #4	$150.96	9.433%	$165.2001	$165.20	$165.20	$165.20
Purchase #5	$131.81	5.765%	$139.4088	$139.41	$139.40	$139.40
Purchase #6	$144.26	12.104%	$161.7212	$161.72	$161.70	$161.70
Purchase #7	$81.66	10.824%	$90.4989	$90.50	$90.50	$90.50
7 purchase totals =	$819.24		$880.3622	$880.37	$880.35	$880.30