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	$78.95	4.234%	$82.2927	$82.29	$82.30	$82.30
Purchase #2	$169.68	11.659%	$189.463	$189.46	$189.45	$189.50
Purchase #3	$219.55	11.239%	$244.2252	$244.23	$244.25	$244.20
Purchase #4	$135.63	13.767%	$154.3022	$154.30	$154.30	$154.30
Purchase #5	$96.91	6.610%	$103.3158	$103.32	$103.30	$103.30
Purchase #6	$68.53	11.502%	$76.4123	$76.41	$76.40	$76.40
Purchase #7	$131.95	13.210%	$149.3806	$149.38	$149.40	$149.40
7 purchase totals =	$901.20		$999.3918	$999.39	$999.40	$999.40