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	$67.35	5.205%	$70.8556	$70.86	$70.85	$70.90
Purchase #2	$109.81	12.458%	$123.4901	$123.49	$123.50	$123.50
Purchase #3	$53.38	5.506%	$56.3191	$56.32	$56.30	$56.30
Purchase #4	$37.35	11.612%	$41.6871	$41.69	$41.70	$41.70
Purchase #5	$96.48	13.810%	$109.8039	$109.80	$109.80	$109.80
Purchase #6	$54.25	6.514%	$57.7838	$57.78	$57.80	$57.80
Purchase #7	$195.89	5.173%	$206.0234	$206.02	$206.00	$206.00
7 purchase totals =	$614.51		$665.9630	$665.96	$665.95	$666.00