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	$18.82	6.400%	$20.0245	$20.02	$20.00	$20.00
Purchase #2	$78.44	4.759%	$82.173	$82.17	$82.15	$82.20
Purchase #3	$109.73	7.485%	$117.9433	$117.94	$117.95	$117.90
Purchase #4	$156.98	4.590%	$164.1854	$164.19	$164.20	$164.20
Purchase #5	$247.78	8.812%	$269.6144	$269.61	$269.60	$269.60
Purchase #6	$159.99	11.614%	$178.5712	$178.57	$178.55	$178.60
Purchase #7	$92.38	5.160%	$97.1468	$97.15	$97.15	$97.10
7 purchase totals =	$864.12		$929.6586	$929.65	$929.60	$929.60