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	$70.72	13.753%	$80.4461	$80.45	$80.45	$80.40
Purchase #2	$6.69	4.743%	$7.0073	$7.01	$7.00	$7.00
Purchase #3	$63.57	13.128%	$71.9155	$71.92	$71.90	$71.90
Purchase #4	$63.95	12.560%	$71.9821	$71.98	$72.00	$72.00
Purchase #5	$19.62	6.813%	$20.9567	$20.96	$20.95	$21.00
Purchase #6	$10.90	8.610%	$11.8385	$11.84	$11.85	$11.80
Purchase #7	$213.36	12.747%	$240.557	$240.56	$240.55	$240.60
7 purchase totals =	$448.81		$504.7032	$504.72	$504.70	$504.70