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	$70.75	3.106%	$72.9475	$72.95	$72.95	$72.90
Purchase #2	$123.84	11.232%	$137.7497	$137.75	$137.75	$137.70
Purchase #3	$233.63	4.129%	$243.2766	$243.28	$243.30	$243.30
Purchase #4	$74.31	8.712%	$80.7839	$80.78	$80.80	$80.80
Purchase #5	$246.48	9.226%	$269.2202	$269.22	$269.20	$269.20
Purchase #6	$53.92	6.139%	$57.2301	$57.23	$57.25	$57.20
Purchase #7	$63.60	5.835%	$67.3111	$67.31	$67.30	$67.30
7 purchase totals =	$866.53		$928.5191	$928.52	$928.55	$928.40