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	$35.40	13.350%	$40.1259	$40.13	$40.15	$40.10
Purchase #2	$232.90	9.132%	$254.1684	$254.17	$254.15	$254.20
Purchase #3	$17.38	6.119%	$18.4435	$18.44	$18.45	$18.40
Purchase #4	$148.33	7.826%	$159.9383	$159.94	$159.95	$159.90
Purchase #5	$174.69	11.330%	$194.4824	$194.48	$194.50	$194.50
Purchase #6	$80.80	12.106%	$90.5816	$90.58	$90.60	$90.60
Purchase #7	$109.70	12.662%	$123.5902	$123.59	$123.60	$123.60
7 purchase totals =	$799.20		$881.3303	$881.33	$881.40	$881.30