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	$131.39	12.478%	$147.7848	$147.78	$147.80	$147.80
Purchase #2	$203.39	10.434%	$224.6117	$224.61	$224.60	$224.60
Purchase #3	$181.73	5.446%	$191.627	$191.63	$191.65	$191.60
Purchase #4	$169.35	4.275%	$176.5897	$176.59	$176.60	$176.60
Purchase #5	$112.65	13.701%	$128.0842	$128.08	$128.10	$128.10
Purchase #6	$90.70	6.772%	$96.8422	$96.84	$96.85	$96.80
Purchase #7	$93.73	6.626%	$99.9405	$99.94	$99.95	$99.90
7 purchase totals =	$982.94		$1,065.4801	$1,065.47	$1,065.55	$1,065.40