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	$73.78	13.130%	$83.4673	$83.47	$83.45	$83.50
Purchase #2	$199.81	11.713%	$223.2137	$223.21	$223.20	$223.20
Purchase #3	$65.43	10.594%	$72.3617	$72.36	$72.35	$72.40
Purchase #4	$6.40	8.396%	$6.9373	$6.94	$6.95	$6.90
Purchase #5	$54.76	4.296%	$57.1125	$57.11	$57.10	$57.10
Purchase #6	$171.28	6.157%	$181.8257	$181.83	$181.85	$181.80
Purchase #7	$182.93	6.277%	$194.4125	$194.41	$194.40	$194.40
7 purchase totals =	$754.39		$819.3307	$819.33	$819.30	$819.30