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	$154.60	7.736%	$166.5599	$166.56	$166.55	$166.60
Purchase #2	$170.26	11.720%	$190.2145	$190.21	$190.20	$190.20
Purchase #3	$96.50	12.831%	$108.8819	$108.88	$108.90	$108.90
Purchase #4	$97.33	8.717%	$105.8143	$105.81	$105.80	$105.80
Purchase #5	$103.83	10.680%	$114.919	$114.92	$114.90	$114.90
Purchase #6	$201.92	10.316%	$222.7501	$222.75	$222.75	$222.80
Purchase #7	$28.97	9.695%	$31.7786	$31.78	$31.80	$31.80
7 purchase totals =	$853.41		$940.9183	$940.91	$940.90	$941.00