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	$89.70	13.534%	$101.84	$101.84	$101.85	$101.80
Purchase #2	$160.26	9.237%	$175.0632	$175.06	$175.05	$175.10
Purchase #3	$35.70	12.662%	$40.2203	$40.22	$40.20	$40.20
Purchase #4	$155.61	7.689%	$167.5749	$167.57	$167.55	$167.60
Purchase #5	$35.60	9.224%	$38.8837	$38.88	$38.90	$38.90
Purchase #6	$81.83	9.191%	$89.351	$89.35	$89.35	$89.40
Purchase #7	$136.47	8.277%	$147.7656	$147.77	$147.75	$147.80
7 purchase totals =	$695.17		$760.6987	$760.69	$760.65	$760.80