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	$26.88	12.629%	$30.2747	$30.27	$30.25	$30.30
Purchase #2	$247.87	5.553%	$261.6342	$261.63	$261.65	$261.60
Purchase #3	$75.98	3.737%	$78.8194	$78.82	$78.80	$78.80
Purchase #4	$60.43	8.360%	$65.4819	$65.48	$65.50	$65.50
Purchase #5	$206.34	3.344%	$213.24	$213.24	$213.25	$213.20
Purchase #6	$34.29	8.820%	$37.3144	$37.31	$37.30	$37.30
Purchase #7	$92.85	13.233%	$105.1368	$105.14	$105.15	$105.10
7 purchase totals =	$744.64		$791.9014	$791.89	$791.90	$791.80