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	$115.91	6.461%	$123.3989	$123.40	$123.40	$123.40
Purchase #2	$181.88	12.629%	$204.8496	$204.85	$204.85	$204.80
Purchase #3	$113.50	8.705%	$123.3802	$123.38	$123.40	$123.40
Purchase #4	$92.56	6.399%	$98.4829	$98.48	$98.50	$98.50
Purchase #5	$118.51	10.833%	$131.3482	$131.35	$131.35	$131.30
Purchase #6	$63.97	13.380%	$72.5292	$72.53	$72.55	$72.50
Purchase #7	$78.57	8.530%	$85.272	$85.27	$85.25	$85.30
7 purchase totals =	$764.90		$839.2610	$839.26	$839.30	$839.20