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	$230.57	5.272%	$242.7257	$242.73	$242.75	$242.70
Purchase #2	$55.70	7.416%	$59.8307	$59.83	$59.85	$59.80
Purchase #3	$212.70	10.639%	$235.3292	$235.33	$235.35	$235.30
Purchase #4	$198.55	4.761%	$208.003	$208.00	$208.00	$208.00
Purchase #5	$229.75	10.697%	$254.3264	$254.33	$254.35	$254.30
Purchase #6	$65.69	3.328%	$67.8762	$67.88	$67.90	$67.90
Purchase #7	$15.80	12.741%	$17.8131	$17.81	$17.80	$17.80
7 purchase totals =	$1,008.76		$1,085.9043	$1,085.91	$1,086.00	$1,085.80