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	$183.78	13.345%	$208.3054	$208.31	$208.30	$208.30
Purchase #2	$130.91	8.816%	$142.451	$142.45	$142.45	$142.50
Purchase #3	$52.84	4.702%	$55.3245	$55.32	$55.30	$55.30
Purchase #4	$194.30	7.188%	$208.2663	$208.27	$208.25	$208.30
Purchase #5	$70.91	4.186%	$73.8783	$73.88	$73.90	$73.90
Purchase #6	$105.94	4.127%	$110.3121	$110.31	$110.30	$110.30
Purchase #7	$53.65	3.206%	$55.37	$55.37	$55.35	$55.40
7 purchase totals =	$792.33		$853.9076	$853.91	$853.85	$854.00