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	$137.47	11.508%	$153.29	$153.29	$153.30	$153.30
Purchase #2	$92.31	3.779%	$95.7984	$95.80	$95.80	$95.80
Purchase #3	$233.29	13.368%	$264.4762	$264.48	$264.50	$264.50
Purchase #4	$45.95	9.735%	$50.4232	$50.42	$50.40	$50.40
Purchase #5	$88.60	12.422%	$99.6059	$99.61	$99.60	$99.60
Purchase #6	$7.80	6.576%	$8.3129	$8.31	$8.30	$8.30
Purchase #7	$185.79	3.122%	$191.5904	$191.59	$191.60	$191.60
7 purchase totals =	$791.21		$863.4970	$863.50	$863.50	$863.50