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	$246.39	12.151%	$276.3288	$276.33	$276.35	$276.30
Purchase #2	$86.90	7.219%	$93.1733	$93.17	$93.15	$93.20
Purchase #3	$73.48	11.722%	$82.0933	$82.09	$82.10	$82.10
Purchase #4	$41.41	10.677%	$45.8313	$45.83	$45.85	$45.80
Purchase #5	$12.79	5.869%	$13.5406	$13.54	$13.55	$13.50
Purchase #6	$64.96	8.629%	$70.5654	$70.57	$70.55	$70.60
Purchase #7	$215.39	8.807%	$234.3594	$234.36	$234.35	$234.40
7 purchase totals =	$741.32		$815.8921	$815.89	$815.90	$815.90