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	$111.61	7.502%	$119.983	$119.98	$120.00	$120.00
Purchase #2	$39.64	12.486%	$44.5895	$44.59	$44.60	$44.60
Purchase #3	$190.71	11.432%	$212.512	$212.51	$212.50	$212.50
Purchase #4	$66.78	9.301%	$72.9912	$72.99	$73.00	$73.00
Purchase #5	$92.80	13.661%	$105.4774	$105.48	$105.50	$105.50
Purchase #6	$189.89	10.507%	$209.8417	$209.84	$209.85	$209.80
Purchase #7	$211.29	12.692%	$238.1069	$238.11	$238.10	$238.10
7 purchase totals =	$902.72		$1,003.5017	$1,003.50	$1,003.55	$1,003.50