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	$46.89	10.628%	$51.8735	$51.87	$51.85	$51.90
Purchase #2	$35.88	6.651%	$38.2664	$38.27	$38.25	$38.30
Purchase #3	$53.67	13.503%	$60.9171	$60.92	$60.90	$60.90
Purchase #4	$55.36	12.679%	$62.3791	$62.38	$62.40	$62.40
Purchase #5	$217.63	5.457%	$229.5061	$229.51	$229.50	$229.50
Purchase #6	$213.66	12.762%	$240.9273	$240.93	$240.95	$240.90
Purchase #7	$6.56	10.822%	$7.2699	$7.27	$7.25	$7.30
7 purchase totals =	$629.65		$691.1394	$691.15	$691.10	$691.20