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	$61.59	8.378%	$66.75	$66.75	$66.75	$66.80
Purchase #2	$233.31	4.777%	$244.4552	$244.46	$244.45	$244.50
Purchase #3	$104.82	4.219%	$109.2424	$109.24	$109.25	$109.20
Purchase #4	$37.62	13.126%	$42.558	$42.56	$42.55	$42.60
Purchase #5	$163.48	9.743%	$179.4079	$179.41	$179.40	$179.40
Purchase #6	$127.80	3.225%	$131.9216	$131.92	$131.90	$131.90
Purchase #7	$24.74	6.735%	$26.4062	$26.41	$26.40	$26.40
7 purchase totals =	$753.36		$800.7413	$800.75	$800.70	$800.80