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	$39.62	4.503%	$41.4041	$41.40	$41.40	$41.40
Purchase #2	$196.93	6.417%	$209.567	$209.57	$209.55	$209.60
Purchase #3	$103.84	7.442%	$111.5678	$111.57	$111.55	$111.60
Purchase #4	$41.87	8.439%	$45.4034	$45.40	$45.40	$45.40
Purchase #5	$147.47	13.580%	$167.4964	$167.50	$167.50	$167.50
Purchase #6	$210.61	10.680%	$233.1031	$233.10	$233.10	$233.10
Purchase #7	$157.34	7.642%	$169.3639	$169.36	$169.35	$169.40
7 purchase totals =	$897.68		$977.9057	$977.90	$977.85	$978.00