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	$77.50	6.196%	$82.3019	$82.30	$82.30	$82.30
Purchase #2	$73.43	12.781%	$82.8151	$82.82	$82.80	$82.80
Purchase #3	$179.81	4.146%	$187.2649	$187.26	$187.25	$187.30
Purchase #4	$172.47	5.857%	$182.5716	$182.57	$182.55	$182.60
Purchase #5	$247.57	9.394%	$270.8267	$270.83	$270.85	$270.80
Purchase #6	$120.53	6.804%	$128.7309	$128.73	$128.75	$128.70
Purchase #7	$156.52	9.354%	$171.1609	$171.16	$171.15	$171.20
7 purchase totals =	$1,027.83		$1,105.6720	$1,105.67	$1,105.65	$1,105.70