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	$79.84	4.407%	$83.3585	$83.36	$83.35	$83.40
Purchase #2	$61.33	10.591%	$67.8255	$67.83	$67.85	$67.80
Purchase #3	$55.36	9.168%	$60.4354	$60.44	$60.45	$60.40
Purchase #4	$213.34	5.739%	$225.5836	$225.58	$225.60	$225.60
Purchase #5	$223.28	11.693%	$249.3881	$249.39	$249.40	$249.40
Purchase #6	$136.80	11.785%	$152.9219	$152.92	$152.90	$152.90
Purchase #7	$118.89	10.729%	$131.6457	$131.65	$131.65	$131.60
7 purchase totals =	$888.84		$971.1587	$971.17	$971.20	$971.10