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	$188.96	11.317%	$210.3446	$210.34	$210.35	$210.30
Purchase #2	$114.66	13.846%	$130.5358	$130.54	$130.55	$130.50
Purchase #3	$199.78	4.435%	$208.6402	$208.64	$208.65	$208.60
Purchase #4	$35.83	5.846%	$37.9246	$37.92	$37.90	$37.90
Purchase #5	$149.31	12.548%	$168.0454	$168.05	$168.05	$168.00
Purchase #6	$37.73	11.622%	$42.115	$42.12	$42.10	$42.10
Purchase #7	$128.50	8.379%	$139.267	$139.27	$139.25	$139.30
7 purchase totals =	$854.77		$936.8726	$936.88	$936.85	$936.70