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	$17.35	8.689%	$18.8575	$18.86	$18.85	$18.90
Purchase #2	$83.64	13.137%	$94.6278	$94.63	$94.65	$94.60
Purchase #3	$219.59	8.805%	$238.9249	$238.92	$238.90	$238.90
Purchase #4	$55.35	6.652%	$59.0319	$59.03	$59.05	$59.00
Purchase #5	$87.56	6.817%	$93.529	$93.53	$93.55	$93.50
Purchase #6	$199.50	11.626%	$222.6939	$222.69	$222.70	$222.70
Purchase #7	$203.36	3.228%	$209.9245	$209.92	$209.90	$209.90
7 purchase totals =	$866.35		$937.5895	$937.58	$937.60	$937.50