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	$15.34	13.472%	$17.4066	$17.41	$17.40	$17.40
Purchase #2	$75.56	5.317%	$79.5775	$79.58	$79.60	$79.60
Purchase #3	$32.33	11.107%	$35.9209	$35.92	$35.90	$35.90
Purchase #4	$101.69	11.746%	$113.6345	$113.63	$113.65	$113.60
Purchase #5	$40.48	7.365%	$43.4614	$43.46	$43.45	$43.50
Purchase #6	$57.53	3.414%	$59.4941	$59.49	$59.50	$59.50
Purchase #7	$87.96	13.611%	$99.9322	$99.93	$99.95	$99.90
7 purchase totals =	$410.89		$449.4272	$449.42	$449.45	$449.40