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	$101.71	7.333%	$109.1684	$109.17	$109.15	$109.20
Purchase #2	$76.54	4.534%	$80.0103	$80.01	$80.00	$80.00
Purchase #3	$209.63	5.764%	$221.7131	$221.71	$221.70	$221.70
Purchase #4	$47.72	12.587%	$53.7265	$53.73	$53.75	$53.70
Purchase #5	$112.31	10.282%	$123.8577	$123.86	$123.85	$123.90
Purchase #6	$65.57	12.768%	$73.942	$73.94	$73.95	$73.90
Purchase #7	$13.43	12.493%	$15.1078	$15.11	$15.10	$15.10
7 purchase totals =	$626.91		$677.5258	$677.53	$677.50	$677.50