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	$36.55	6.376%	$38.8804	$38.88	$38.90	$38.90
Purchase #2	$95.64	10.759%	$105.9299	$105.93	$105.95	$105.90
Purchase #3	$236.39	10.361%	$260.8824	$260.88	$260.90	$260.90
Purchase #4	$149.89	10.744%	$165.9942	$165.99	$166.00	$166.00
Purchase #5	$171.34	7.258%	$183.7759	$183.78	$183.80	$183.80
Purchase #6	$93.73	11.512%	$104.5202	$104.52	$104.50	$104.50
Purchase #7	$212.27	5.501%	$223.947	$223.95	$223.95	$223.90
7 purchase totals =	$995.81		$1,083.9300	$1,083.93	$1,084.00	$1,083.90