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	$130.59	4.667%	$136.6846	$136.68	$136.70	$136.70
Purchase #2	$149.85	3.603%	$155.2491	$155.25	$155.25	$155.20
Purchase #3	$31.77	11.817%	$35.5243	$35.52	$35.50	$35.50
Purchase #4	$159.74	7.437%	$171.6199	$171.62	$171.60	$171.60
Purchase #5	$141.60	10.511%	$156.4836	$156.48	$156.50	$156.50
Purchase #6	$154.80	10.648%	$171.2831	$171.28	$171.30	$171.30
Purchase #7	$31.88	3.549%	$33.0114	$33.01	$33.00	$33.00
7 purchase totals =	$800.23		$859.8560	$859.84	$859.85	$859.80