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	$147.76	4.619%	$154.585	$154.59	$154.60	$154.60
Purchase #2	$58.93	9.350%	$64.44	$64.44	$64.45	$64.40
Purchase #3	$18.60	6.612%	$19.8298	$19.83	$19.85	$19.80
Purchase #4	$52.72	4.535%	$55.1109	$55.11	$55.10	$55.10
Purchase #5	$194.66	8.661%	$211.5195	$211.52	$211.50	$211.50
Purchase #6	$198.26	12.427%	$222.8978	$222.90	$222.90	$222.90
Purchase #7	$188.41	13.105%	$213.1011	$213.10	$213.10	$213.10
7 purchase totals =	$859.34		$941.4841	$941.49	$941.50	$941.40