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	$59.92	11.441%	$66.7754	$66.78	$66.80	$66.80
Purchase #2	$148.55	10.558%	$164.2339	$164.23	$164.25	$164.20
Purchase #3	$83.37	8.204%	$90.2097	$90.21	$90.20	$90.20
Purchase #4	$37.59	5.655%	$39.7157	$39.72	$39.70	$39.70
Purchase #5	$155.64	8.524%	$168.9068	$168.91	$168.90	$168.90
Purchase #6	$126.56	6.476%	$134.756	$134.76	$134.75	$134.80
Purchase #7	$54.42	5.281%	$57.2939	$57.29	$57.30	$57.30
7 purchase totals =	$666.05		$721.8914	$721.90	$721.90	$721.90