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	$7.52	10.329%	$8.2967	$8.30	$8.30	$8.30
Purchase #2	$90.45	4.232%	$94.2778	$94.28	$94.30	$94.30
Purchase #3	$116.74	11.410%	$130.06	$130.06	$130.05	$130.10
Purchase #4	$110.95	5.618%	$117.1832	$117.18	$117.20	$117.20
Purchase #5	$71.30	9.818%	$78.3002	$78.30	$78.30	$78.30
Purchase #6	$136.59	3.820%	$141.8077	$141.81	$141.80	$141.80
Purchase #7	$250.92	11.365%	$279.4371	$279.44	$279.45	$279.40
7 purchase totals =	$784.47		$849.3627	$849.37	$849.40	$849.40