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	$84.70	6.701%	$90.3757	$90.38	$90.40	$90.40
Purchase #2	$10.60	6.527%	$11.2919	$11.29	$11.30	$11.30
Purchase #3	$69.43	13.459%	$78.7746	$78.77	$78.75	$78.80
Purchase #4	$159.42	6.144%	$169.2148	$169.21	$169.20	$169.20
Purchase #5	$61.85	9.212%	$67.5476	$67.55	$67.55	$67.50
Purchase #6	$239.33	7.357%	$256.9375	$256.94	$256.95	$256.90
Purchase #7	$216.87	12.297%	$243.5385	$243.54	$243.55	$243.50
7 purchase totals =	$842.20		$917.6806	$917.68	$917.70	$917.60