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	$131.82	13.312%	$149.3679	$149.37	$149.35	$149.40
Purchase #2	$112.53	12.861%	$127.0025	$127.00	$127.00	$127.00
Purchase #3	$237.34	9.404%	$259.6595	$259.66	$259.65	$259.70
Purchase #4	$110.78	8.197%	$119.8606	$119.86	$119.85	$119.90
Purchase #5	$16.47	10.184%	$18.1473	$18.15	$18.15	$18.10
Purchase #6	$146.41	10.838%	$162.2779	$162.28	$162.30	$162.30
Purchase #7	$68.76	6.113%	$72.9633	$72.96	$72.95	$73.00
7 purchase totals =	$824.11		$909.2790	$909.28	$909.25	$909.40