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	$225.93	5.247%	$237.7845	$237.78	$237.80	$237.80
Purchase #2	$152.87	4.680%	$160.0243	$160.02	$160.00	$160.00
Purchase #3	$125.73	10.809%	$139.3202	$139.32	$139.30	$139.30
Purchase #4	$185.30	13.307%	$209.9579	$209.96	$209.95	$210.00
Purchase #5	$109.73	9.260%	$119.891	$119.89	$119.90	$119.90
Purchase #6	$218.73	10.556%	$241.8191	$241.82	$241.80	$241.80
Purchase #7	$179.88	6.487%	$191.5488	$191.55	$191.55	$191.50
7 purchase totals =	$1,198.17		$1,300.3458	$1,300.34	$1,300.30	$1,300.30