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	$130.33	8.448%	$141.3403	$141.34	$141.35	$141.30
Purchase #2	$126.46	8.580%	$137.3103	$137.31	$137.30	$137.30
Purchase #3	$65.33	10.168%	$71.9728	$71.97	$71.95	$72.00
Purchase #4	$131.81	4.203%	$137.35	$137.35	$137.35	$137.40
Purchase #5	$186.90	5.267%	$196.744	$196.74	$196.75	$196.70
Purchase #6	$121.96	7.296%	$130.8582	$130.86	$130.85	$130.90
Purchase #7	$54.66	6.678%	$58.3102	$58.31	$58.30	$58.30
7 purchase totals =	$817.45		$873.8858	$873.88	$873.85	$873.90