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	$69.47	12.542%	$78.1829	$78.18	$78.20	$78.20
Purchase #2	$204.88	8.102%	$221.4794	$221.48	$221.50	$221.50
Purchase #3	$31.39	3.123%	$32.3703	$32.37	$32.35	$32.40
Purchase #4	$67.26	9.446%	$73.6134	$73.61	$73.60	$73.60
Purchase #5	$101.36	4.437%	$105.8573	$105.86	$105.85	$105.90
Purchase #6	$5.33	7.471%	$5.7282	$5.73	$5.75	$5.70
Purchase #7	$99.79	3.354%	$103.137	$103.14	$103.15	$103.10
7 purchase totals =	$579.48		$620.3685	$620.37	$620.40	$620.40