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	$99.45	11.327%	$110.7147	$110.71	$110.70	$110.70
Purchase #2	$95.77	5.241%	$100.7893	$100.79	$100.80	$100.80
Purchase #3	$242.44	13.635%	$275.4967	$275.50	$275.50	$275.50
Purchase #4	$149.42	11.427%	$166.4942	$166.49	$166.50	$166.50
Purchase #5	$20.57	3.644%	$21.3196	$21.32	$21.30	$21.30
Purchase #6	$160.40	13.544%	$182.1246	$182.12	$182.10	$182.10
Purchase #7	$189.96	12.387%	$213.4903	$213.49	$213.50	$213.50
7 purchase totals =	$958.01		$1,070.4294	$1,070.42	$1,070.40	$1,070.40