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	$60.59	6.574%	$64.5732	$64.57	$64.55	$64.60
Purchase #2	$96.37	3.246%	$99.4982	$99.50	$99.50	$99.50
Purchase #3	$45.66	7.111%	$48.9069	$48.91	$48.90	$48.90
Purchase #4	$218.47	8.821%	$237.7412	$237.74	$237.75	$237.70
Purchase #5	$223.76	11.547%	$249.5976	$249.60	$249.60	$249.60
Purchase #6	$232.96	5.457%	$245.6726	$245.67	$245.65	$245.70
Purchase #7	$125.48	9.540%	$137.4508	$137.45	$137.45	$137.50
7 purchase totals =	$1,003.29		$1,083.4405	$1,083.44	$1,083.40	$1,083.50