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	$85.38	4.486%	$89.2101	$89.21	$89.20	$89.20
Purchase #2	$184.53	6.327%	$196.2052	$196.21	$196.20	$196.20
Purchase #3	$104.49	9.497%	$114.4134	$114.41	$114.40	$114.40
Purchase #4	$76.37	6.333%	$81.2065	$81.21	$81.20	$81.20
Purchase #5	$6.75	4.419%	$7.0483	$7.05	$7.05	$7.00
Purchase #6	$75.38	13.672%	$85.686	$85.69	$85.70	$85.70
Purchase #7	$226.55	4.534%	$236.8218	$236.82	$236.80	$236.80
7 purchase totals =	$759.45		$810.5913	$810.60	$810.55	$810.50