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	$73.85	3.160%	$76.1837	$76.18	$76.20	$76.20
Purchase #2	$63.71	6.789%	$68.0353	$68.04	$68.05	$68.00
Purchase #3	$81.56	12.612%	$91.8463	$91.85	$91.85	$91.80
Purchase #4	$43.46	6.211%	$46.1593	$46.16	$46.15	$46.20
Purchase #5	$93.59	7.331%	$100.4511	$100.45	$100.45	$100.50
Purchase #6	$116.67	9.616%	$127.889	$127.89	$127.90	$127.90
Purchase #7	$72.43	7.851%	$78.1165	$78.12	$78.10	$78.10
7 purchase totals =	$545.27		$588.6812	$588.69	$588.70	$588.70