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	$80.59	11.104%	$89.5387	$89.54	$89.55	$89.50
Purchase #2	$184.34	12.352%	$207.1097	$207.11	$207.10	$207.10
Purchase #3	$51.37	4.761%	$53.8157	$53.82	$53.80	$53.80
Purchase #4	$45.77	3.809%	$47.5134	$47.51	$47.50	$47.50
Purchase #5	$97.59	7.654%	$105.0595	$105.06	$105.05	$105.10
Purchase #6	$121.61	12.488%	$136.7967	$136.80	$136.80	$136.80
Purchase #7	$18.36	13.776%	$20.8893	$20.89	$20.90	$20.90
7 purchase totals =	$599.63		$660.7230	$660.73	$660.70	$660.70