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	$54.56	8.118%	$58.9892	$58.99	$59.00	$59.00
Purchase #2	$129.58	8.237%	$140.2535	$140.25	$140.25	$140.30
Purchase #3	$160.52	6.869%	$171.5461	$171.55	$171.55	$171.50
Purchase #4	$210.58	13.287%	$238.5598	$238.56	$238.55	$238.60
Purchase #5	$16.41	13.261%	$18.5861	$18.59	$18.60	$18.60
Purchase #6	$155.90	6.591%	$166.1754	$166.18	$166.20	$166.20
Purchase #7	$41.40	3.645%	$42.909	$42.91	$42.90	$42.90
7 purchase totals =	$768.95		$837.0191	$837.03	$837.05	$837.10