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	$6.90	3.476%	$7.1398	$7.14	$7.15	$7.10
Purchase #2	$72.84	9.851%	$80.0155	$80.02	$80.00	$80.00
Purchase #3	$56.89	8.256%	$61.5868	$61.59	$61.60	$61.60
Purchase #4	$102.78	3.858%	$106.7453	$106.75	$106.75	$106.70
Purchase #5	$167.48	7.555%	$180.1331	$180.13	$180.15	$180.10
Purchase #6	$99.94	13.639%	$113.5708	$113.57	$113.55	$113.60
Purchase #7	$81.51	6.501%	$86.809	$86.81	$86.80	$86.80
7 purchase totals =	$588.34		$636.0003	$636.01	$636.00	$635.90