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	$179.60	11.442%	$200.1498	$200.15	$200.15	$200.10
Purchase #2	$173.30	6.353%	$184.3097	$184.31	$184.30	$184.30
Purchase #3	$121.78	12.383%	$136.86	$136.86	$136.85	$136.90
Purchase #4	$237.86	11.230%	$264.5717	$264.57	$264.55	$264.60
Purchase #5	$215.28	11.490%	$240.0157	$240.02	$240.00	$240.00
Purchase #6	$12.90	11.626%	$14.3998	$14.40	$14.40	$14.40
Purchase #7	$35.26	13.281%	$39.9429	$39.94	$39.95	$39.90
7 purchase totals =	$975.98		$1,080.2496	$1,080.25	$1,080.20	$1,080.20