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	$54.78	8.610%	$59.4966	$59.50	$59.50	$59.50
Purchase #2	$52.26	3.263%	$53.9652	$53.97	$53.95	$54.00
Purchase #3	$210.83	3.298%	$217.7832	$217.78	$217.80	$217.80
Purchase #4	$157.74	12.300%	$177.142	$177.14	$177.15	$177.10
Purchase #5	$47.40	5.725%	$50.1137	$50.11	$50.10	$50.10
Purchase #6	$64.36	11.586%	$71.8167	$71.82	$71.80	$71.80
Purchase #7	$179.94	4.619%	$188.2514	$188.25	$188.25	$188.30
7 purchase totals =	$767.31		$818.5688	$818.57	$818.55	$818.60