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	$135.32	6.262%	$143.7937	$143.79	$143.80	$143.80
Purchase #2	$112.63	3.110%	$116.1328	$116.13	$116.15	$116.10
Purchase #3	$94.77	7.302%	$101.6901	$101.69	$101.70	$101.70
Purchase #4	$216.46	3.337%	$223.6833	$223.68	$223.70	$223.70
Purchase #5	$104.46	11.831%	$116.8187	$116.82	$116.80	$116.80
Purchase #6	$72.97	13.589%	$82.8859	$82.89	$82.90	$82.90
Purchase #7	$70.34	11.211%	$78.2258	$78.23	$78.25	$78.20
7 purchase totals =	$806.95		$863.2303	$863.23	$863.30	$863.20