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	$151.66	13.352%	$171.9096	$171.91	$171.90	$171.90
Purchase #2	$141.60	6.341%	$150.5789	$150.58	$150.60	$150.60
Purchase #3	$72.45	8.577%	$78.664	$78.66	$78.65	$78.70
Purchase #4	$169.55	10.511%	$187.3714	$187.37	$187.35	$187.40
Purchase #5	$83.40	7.385%	$89.5591	$89.56	$89.55	$89.60
Purchase #6	$95.95	13.794%	$109.1853	$109.19	$109.20	$109.20
Purchase #7	$50.50	13.406%	$57.27	$57.27	$57.25	$57.30
7 purchase totals =	$765.11		$844.5383	$844.54	$844.50	$844.70