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	$242.53	6.594%	$258.5224	$258.52	$258.50	$258.50
Purchase #2	$122.33	7.206%	$131.1451	$131.15	$131.15	$131.10
Purchase #3	$95.30	3.511%	$98.646	$98.65	$98.65	$98.60
Purchase #4	$128.71	11.835%	$143.9428	$143.94	$143.95	$143.90
Purchase #5	$30.38	11.115%	$33.7567	$33.76	$33.75	$33.80
Purchase #6	$88.60	9.102%	$96.6644	$96.66	$96.65	$96.70
Purchase #7	$128.37	13.556%	$145.7718	$145.77	$145.75	$145.80
7 purchase totals =	$836.22		$908.4492	$908.45	$908.40	$908.40