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	$162.71	13.713%	$185.0224	$185.02	$185.00	$185.00
Purchase #2	$27.47	9.742%	$30.1461	$30.15	$30.15	$30.10
Purchase #3	$96.51	3.301%	$99.6958	$99.70	$99.70	$99.70
Purchase #4	$53.32	12.141%	$59.7936	$59.79	$59.80	$59.80
Purchase #5	$81.36	9.722%	$89.2698	$89.27	$89.25	$89.30
Purchase #6	$187.49	8.756%	$203.9066	$203.91	$203.90	$203.90
Purchase #7	$105.62	9.653%	$115.8155	$115.82	$115.80	$115.80
7 purchase totals =	$714.48		$783.6498	$783.66	$783.60	$783.60