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	$185.62	12.789%	$209.3589	$209.36	$209.35	$209.40
Purchase #2	$196.60	13.384%	$222.9129	$222.91	$222.90	$222.90
Purchase #3	$220.91	11.336%	$245.9524	$245.95	$245.95	$246.00
Purchase #4	$84.48	6.818%	$90.2398	$90.24	$90.25	$90.20
Purchase #5	$26.38	8.191%	$28.5408	$28.54	$28.55	$28.50
Purchase #6	$151.83	5.756%	$160.5693	$160.57	$160.55	$160.60
Purchase #7	$208.76	6.347%	$222.01	$222.01	$222.00	$222.00
7 purchase totals =	$1,074.58		$1,179.5841	$1,179.58	$1,179.55	$1,179.60