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	$67.54	3.684%	$70.0282	$70.03	$70.05	$70.00
Purchase #2	$176.82	11.230%	$196.6769	$196.68	$196.70	$196.70
Purchase #3	$85.58	7.822%	$92.2741	$92.27	$92.25	$92.30
Purchase #4	$54.68	8.114%	$59.1167	$59.12	$59.10	$59.10
Purchase #5	$98.93	4.368%	$103.2513	$103.25	$103.25	$103.30
Purchase #6	$150.59	3.853%	$156.3922	$156.39	$156.40	$156.40
Purchase #7	$83.54	11.604%	$93.234	$93.23	$93.25	$93.20
7 purchase totals =	$717.68		$770.9734	$770.97	$771.00	$771.00