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	$124.50	5.329%	$131.1346	$131.13	$131.15	$131.10
Purchase #2	$145.74	4.444%	$152.2167	$152.22	$152.20	$152.20
Purchase #3	$19.92	7.337%	$21.3815	$21.38	$21.40	$21.40
Purchase #4	$83.96	6.190%	$89.1571	$89.16	$89.15	$89.20
Purchase #5	$59.80	12.635%	$67.3557	$67.36	$67.35	$67.40
Purchase #6	$30.28	9.874%	$33.2698	$33.27	$33.25	$33.30
Purchase #7	$44.35	8.864%	$48.2812	$48.28	$48.30	$48.30
7 purchase totals =	$508.55		$542.7966	$542.80	$542.80	$542.90