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	$71.84	9.348%	$78.5556	$78.56	$78.55	$78.60
Purchase #2	$39.75	8.570%	$43.1566	$43.16	$43.15	$43.20
Purchase #3	$47.79	6.428%	$50.8619	$50.86	$50.85	$50.90
Purchase #4	$133.63	13.360%	$151.483	$151.48	$151.50	$151.50
Purchase #5	$242.35	8.797%	$263.6695	$263.67	$263.65	$263.70
Purchase #6	$132.53	4.815%	$138.9113	$138.91	$138.90	$138.90
Purchase #7	$138.89	11.731%	$155.1832	$155.18	$155.20	$155.20
7 purchase totals =	$806.78		$881.8211	$881.82	$881.80	$882.00