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	$114.82	7.380%	$123.2937	$123.29	$123.30	$123.30
Purchase #2	$97.69	7.709%	$105.2209	$105.22	$105.20	$105.20
Purchase #3	$54.76	8.473%	$59.3998	$59.40	$59.40	$59.40
Purchase #4	$17.63	3.210%	$18.1959	$18.20	$18.20	$18.20
Purchase #5	$151.77	10.557%	$167.7924	$167.79	$167.80	$167.80
Purchase #6	$30.25	12.279%	$33.9644	$33.96	$33.95	$34.00
Purchase #7	$10.52	12.115%	$11.7945	$11.79	$11.80	$11.80
7 purchase totals =	$477.44		$519.6616	$519.65	$519.65	$519.70