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	$35.49	9.393%	$38.8236	$38.82	$38.80	$38.80
Purchase #2	$125.57	4.648%	$131.4065	$131.41	$131.40	$131.40
Purchase #3	$61.48	11.402%	$68.4899	$68.49	$68.50	$68.50
Purchase #4	$6.29	3.868%	$6.5333	$6.53	$6.55	$6.50
Purchase #5	$9.77	11.221%	$10.8663	$10.87	$10.85	$10.90
Purchase #6	$239.94	5.798%	$253.8517	$253.85	$253.85	$253.90
Purchase #7	$188.33	4.183%	$196.2078	$196.21	$196.20	$196.20
7 purchase totals =	$666.87		$706.1791	$706.18	$706.15	$706.20