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	$19.80	13.232%	$22.4199	$22.42	$22.40	$22.40
Purchase #2	$208.94	6.193%	$221.8797	$221.88	$221.90	$221.90
Purchase #3	$145.47	7.865%	$156.9112	$156.91	$156.90	$156.90
Purchase #4	$127.71	9.850%	$140.2894	$140.29	$140.30	$140.30
Purchase #5	$205.50	8.747%	$223.4751	$223.48	$223.50	$223.50
Purchase #6	$209.89	4.191%	$218.6865	$218.69	$218.70	$218.70
Purchase #7	$151.38	8.417%	$164.1217	$164.12	$164.10	$164.10
7 purchase totals =	$1,068.69		$1,147.7835	$1,147.79	$1,147.80	$1,147.80