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	$80.91	11.377%	$90.1151	$90.12	$90.10	$90.10
Purchase #2	$213.50	9.505%	$233.7932	$233.79	$233.80	$233.80
Purchase #3	$136.59	11.352%	$152.0957	$152.10	$152.10	$152.10
Purchase #4	$250.87	7.125%	$268.7445	$268.74	$268.75	$268.70
Purchase #5	$151.25	4.778%	$158.4767	$158.48	$158.50	$158.50
Purchase #6	$250.29	7.777%	$269.7551	$269.76	$269.75	$269.80
Purchase #7	$11.98	12.653%	$13.4958	$13.50	$13.50	$13.50
7 purchase totals =	$1,095.39		$1,186.4761	$1,186.49	$1,186.50	$1,186.50