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	$118.28	4.740%	$123.8865	$123.89	$123.90	$123.90
Purchase #2	$165.43	12.601%	$186.2758	$186.28	$186.30	$186.30
Purchase #3	$116.31	10.415%	$128.4237	$128.42	$128.40	$128.40
Purchase #4	$82.37	3.526%	$85.2744	$85.27	$85.25	$85.30
Purchase #5	$13.79	9.735%	$15.1325	$15.13	$15.15	$15.10
Purchase #6	$228.73	5.291%	$240.8321	$240.83	$240.85	$240.80
Purchase #7	$120.62	7.729%	$129.9427	$129.94	$129.95	$129.90
7 purchase totals =	$845.53		$909.7677	$909.76	$909.80	$909.70