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	$29.56	5.704%	$31.2461	$31.25	$31.25	$31.20
Purchase #2	$233.28	6.216%	$247.7807	$247.78	$247.80	$247.80
Purchase #3	$38.56	6.239%	$40.9658	$40.97	$40.95	$41.00
Purchase #4	$221.61	11.402%	$246.878	$246.88	$246.90	$246.90
Purchase #5	$59.89	12.788%	$67.5487	$67.55	$67.55	$67.50
Purchase #6	$231.52	3.590%	$239.8316	$239.83	$239.85	$239.80
Purchase #7	$94.25	13.365%	$106.8465	$106.85	$106.85	$106.80
7 purchase totals =	$908.67		$981.0974	$981.11	$981.15	$981.00