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	$70.99	10.533%	$78.4674	$78.47	$78.45	$78.50
Purchase #2	$215.51	12.734%	$242.953	$242.95	$242.95	$243.00
Purchase #3	$172.59	11.181%	$191.8873	$191.89	$191.90	$191.90
Purchase #4	$140.51	6.429%	$149.5434	$149.54	$149.55	$149.50
Purchase #5	$30.98	7.665%	$33.3546	$33.35	$33.35	$33.40
Purchase #6	$57.31	13.199%	$64.8743	$64.87	$64.85	$64.90
Purchase #7	$249.81	3.862%	$259.4577	$259.46	$259.45	$259.50
7 purchase totals =	$937.70		$1,020.5377	$1,020.53	$1,020.50	$1,020.70