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	$55.89	6.457%	$59.4988	$59.50	$59.50	$59.50
Purchase #2	$227.75	12.789%	$256.8769	$256.88	$256.90	$256.90
Purchase #3	$238.59	4.874%	$250.2189	$250.22	$250.20	$250.20
Purchase #4	$176.61	4.241%	$184.1	$184.10	$184.10	$184.10
Purchase #5	$200.46	3.137%	$206.7484	$206.75	$206.75	$206.70
Purchase #6	$43.72	5.590%	$46.1639	$46.16	$46.15	$46.20
Purchase #7	$233.33	7.300%	$250.3631	$250.36	$250.35	$250.40
7 purchase totals =	$1,176.35		$1,253.9700	$1,253.97	$1,253.95	$1,254.00