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	$109.50	13.221%	$123.977	$123.98	$124.00	$124.00
Purchase #2	$188.39	4.535%	$196.9335	$196.93	$196.95	$196.90
Purchase #3	$17.80	6.250%	$18.9125	$18.91	$18.90	$18.90
Purchase #4	$197.35	11.287%	$219.6249	$219.62	$219.60	$219.60
Purchase #5	$242.59	3.252%	$250.479	$250.48	$250.50	$250.50
Purchase #6	$40.67	4.103%	$42.3387	$42.34	$42.35	$42.30
Purchase #7	$33.71	5.546%	$35.5796	$35.58	$35.60	$35.60
7 purchase totals =	$830.01		$887.8452	$887.84	$887.90	$887.80