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	$82.93	7.705%	$89.3198	$89.32	$89.30	$89.30
Purchase #2	$12.50	6.561%	$13.3201	$13.32	$13.30	$13.30
Purchase #3	$129.27	13.659%	$146.927	$146.93	$146.95	$146.90
Purchase #4	$213.83	13.643%	$243.0028	$243.00	$243.00	$243.00
Purchase #5	$203.66	11.532%	$227.1461	$227.15	$227.15	$227.10
Purchase #6	$91.57	9.744%	$100.4926	$100.49	$100.50	$100.50
Purchase #7	$110.35	8.541%	$119.775	$119.78	$119.80	$119.80
7 purchase totals =	$844.11		$939.9834	$939.99	$940.00	$939.90