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	$131.46	12.315%	$147.6493	$147.65	$147.65	$147.60
Purchase #2	$172.58	11.166%	$191.8503	$191.85	$191.85	$191.90
Purchase #3	$152.47	7.657%	$164.1446	$164.14	$164.15	$164.10
Purchase #4	$30.43	4.226%	$31.716	$31.72	$31.70	$31.70
Purchase #5	$117.37	13.463%	$133.1715	$133.17	$133.15	$133.20
Purchase #6	$183.73	9.321%	$200.8555	$200.86	$200.85	$200.90
Purchase #7	$16.69	11.635%	$18.6319	$18.63	$18.65	$18.60
7 purchase totals =	$804.73		$888.0191	$888.02	$888.00	$888.00