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	$218.33	13.352%	$247.4814	$247.48	$247.50	$247.50
Purchase #2	$135.40	5.195%	$142.434	$142.43	$142.45	$142.40
Purchase #3	$180.89	9.489%	$198.0547	$198.05	$198.05	$198.10
Purchase #4	$157.67	5.635%	$166.5547	$166.55	$166.55	$166.60
Purchase #5	$111.30	4.147%	$115.9156	$115.92	$115.90	$115.90
Purchase #6	$219.46	6.597%	$233.9378	$233.94	$233.95	$233.90
Purchase #7	$60.62	10.707%	$67.1106	$67.11	$67.10	$67.10
7 purchase totals =	$1,083.67		$1,171.4888	$1,171.48	$1,171.50	$1,171.50