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	$187.96	13.756%	$213.8158	$213.82	$213.80	$213.80
Purchase #2	$48.81	9.364%	$53.3806	$53.38	$53.40	$53.40
Purchase #3	$53.55	10.511%	$59.1786	$59.18	$59.20	$59.20
Purchase #4	$31.47	7.171%	$33.7267	$33.73	$33.75	$33.70
Purchase #5	$104.83	3.665%	$108.672	$108.67	$108.65	$108.70
Purchase #6	$89.88	7.214%	$96.3639	$96.36	$96.35	$96.40
Purchase #7	$70.47	12.326%	$79.1561	$79.16	$79.15	$79.20
7 purchase totals =	$586.97		$644.2937	$644.30	$644.30	$644.40