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	$129.46	12.407%	$145.5221	$145.52	$145.50	$145.50
Purchase #2	$82.74	10.413%	$91.3557	$91.36	$91.35	$91.40
Purchase #3	$242.95	4.474%	$253.8196	$253.82	$253.80	$253.80
Purchase #4	$5.59	4.647%	$5.8498	$5.85	$5.85	$5.80
Purchase #5	$155.86	7.844%	$168.0857	$168.09	$168.10	$168.10
Purchase #6	$101.48	4.383%	$105.9279	$105.93	$105.95	$105.90
Purchase #7	$150.34	10.256%	$165.7589	$165.76	$165.75	$165.80
7 purchase totals =	$868.42		$936.3197	$936.33	$936.30	$936.30