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	$30.35	5.820%	$32.1164	$32.12	$32.10	$32.10
Purchase #2	$147.48	11.612%	$164.6054	$164.61	$164.60	$164.60
Purchase #3	$18.89	6.622%	$20.1409	$20.14	$20.15	$20.10
Purchase #4	$97.39	12.789%	$109.8452	$109.85	$109.85	$109.80
Purchase #5	$180.74	4.617%	$189.0848	$189.08	$189.10	$189.10
Purchase #6	$186.86	3.675%	$193.7271	$193.73	$193.75	$193.70
Purchase #7	$174.47	4.579%	$182.459	$182.46	$182.45	$182.50
7 purchase totals =	$836.18		$891.9788	$891.99	$892.00	$891.90