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	$73.82	6.192%	$78.3909	$78.39	$78.40	$78.40
Purchase #2	$80.91	6.147%	$85.8835	$85.88	$85.90	$85.90
Purchase #3	$240.84	6.446%	$256.3645	$256.36	$256.35	$256.40
Purchase #4	$163.72	4.319%	$170.7911	$170.79	$170.80	$170.80
Purchase #5	$195.55	6.742%	$208.734	$208.73	$208.75	$208.70
Purchase #6	$95.93	9.772%	$105.3043	$105.30	$105.30	$105.30
Purchase #7	$20.98	8.806%	$22.8275	$22.83	$22.85	$22.80
7 purchase totals =	$871.75		$928.2958	$928.28	$928.35	$928.30