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	$153.56	8.357%	$166.393	$166.39	$166.40	$166.40
Purchase #2	$155.69	6.843%	$166.3439	$166.34	$166.35	$166.30
Purchase #3	$136.98	7.851%	$147.7343	$147.73	$147.75	$147.70
Purchase #4	$237.37	13.601%	$269.6547	$269.65	$269.65	$269.70
Purchase #5	$27.48	13.517%	$31.1945	$31.19	$31.20	$31.20
Purchase #6	$75.45	4.605%	$78.9245	$78.92	$78.90	$78.90
Purchase #7	$212.50	7.402%	$228.2293	$228.23	$228.25	$228.20
7 purchase totals =	$999.03		$1,088.4742	$1,088.45	$1,088.50	$1,088.40