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	$71.89	13.657%	$81.708	$81.71	$81.70	$81.70
Purchase #2	$136.70	11.800%	$152.8306	$152.83	$152.85	$152.80
Purchase #3	$248.28	12.740%	$279.9109	$279.91	$279.90	$279.90
Purchase #4	$96.64	5.125%	$101.5928	$101.59	$101.60	$101.60
Purchase #5	$88.77	8.746%	$96.5338	$96.53	$96.55	$96.50
Purchase #6	$38.51	11.234%	$42.8362	$42.84	$42.85	$42.80
Purchase #7	$96.81	13.770%	$110.1407	$110.14	$110.15	$110.10
7 purchase totals =	$777.60		$865.5530	$865.55	$865.60	$865.40