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	$68.97	13.205%	$78.0775	$78.08	$78.10	$78.10
Purchase #2	$40.95	3.656%	$42.4471	$42.45	$42.45	$42.40
Purchase #3	$130.67	8.134%	$141.2987	$141.30	$141.30	$141.30
Purchase #4	$203.50	9.712%	$223.2639	$223.26	$223.25	$223.30
Purchase #5	$30.28	6.153%	$32.1431	$32.14	$32.15	$32.10
Purchase #6	$234.78	12.315%	$263.6932	$263.69	$263.70	$263.70
Purchase #7	$28.83	8.855%	$31.3829	$31.38	$31.40	$31.40
7 purchase totals =	$737.98		$812.3064	$812.30	$812.35	$812.30