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	$212.88	5.847%	$225.3271	$225.33	$225.35	$225.30
Purchase #2	$86.77	7.629%	$93.3897	$93.39	$93.40	$93.40
Purchase #3	$92.40	11.448%	$102.978	$102.98	$103.00	$103.00
Purchase #4	$56.49	5.275%	$59.4698	$59.47	$59.45	$59.50
Purchase #5	$130.74	6.202%	$138.8485	$138.85	$138.85	$138.80
Purchase #6	$190.38	12.342%	$213.8767	$213.88	$213.90	$213.90
Purchase #7	$74.87	8.801%	$81.4593	$81.46	$81.45	$81.50
7 purchase totals =	$844.53		$915.3491	$915.36	$915.40	$915.40