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	$54.93	7.364%	$58.975	$58.98	$59.00	$59.00
Purchase #2	$150.97	4.350%	$157.5372	$157.54	$157.55	$157.50
Purchase #3	$47.62	12.618%	$53.6287	$53.63	$53.65	$53.60
Purchase #4	$54.86	7.837%	$59.1594	$59.16	$59.15	$59.20
Purchase #5	$107.42	8.676%	$116.7398	$116.74	$116.75	$116.70
Purchase #6	$85.46	7.556%	$91.9174	$91.92	$91.90	$91.90
Purchase #7	$170.47	8.295%	$184.6105	$184.61	$184.60	$184.60
7 purchase totals =	$671.73		$722.5680	$722.58	$722.60	$722.50