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	$71.53	9.759%	$78.5106	$78.51	$78.50	$78.50
Purchase #2	$244.45	9.788%	$268.3768	$268.38	$268.40	$268.40
Purchase #3	$84.37	12.416%	$94.8454	$94.85	$94.85	$94.80
Purchase #4	$135.61	10.516%	$149.8707	$149.87	$149.85	$149.90
Purchase #5	$171.26	9.116%	$186.8721	$186.87	$186.85	$186.90
Purchase #6	$143.51	6.262%	$152.4966	$152.50	$152.50	$152.50
Purchase #7	$195.28	12.535%	$219.7583	$219.76	$219.75	$219.80
7 purchase totals =	$1,046.01		$1,150.7305	$1,150.74	$1,150.70	$1,150.80