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	$202.75	6.461%	$215.8497	$215.85	$215.85	$215.80
Purchase #2	$208.31	12.762%	$234.8945	$234.89	$234.90	$234.90
Purchase #3	$39.74	7.113%	$42.5667	$42.57	$42.55	$42.60
Purchase #4	$141.46	13.177%	$160.1002	$160.10	$160.10	$160.10
Purchase #5	$94.44	13.473%	$107.1639	$107.16	$107.15	$107.20
Purchase #6	$159.75	7.574%	$171.8495	$171.85	$171.85	$171.80
Purchase #7	$76.34	8.500%	$82.8289	$82.83	$82.85	$82.80
7 purchase totals =	$922.79		$1,015.2534	$1,015.25	$1,015.25	$1,015.20