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	$66.67	7.299%	$71.5362	$71.54	$71.55	$71.50
Purchase #2	$82.65	3.155%	$85.2576	$85.26	$85.25	$85.30
Purchase #3	$186.91	12.465%	$210.2083	$210.21	$210.20	$210.20
Purchase #4	$235.38	6.564%	$250.8303	$250.83	$250.85	$250.80
Purchase #5	$37.99	11.690%	$42.431	$42.43	$42.45	$42.40
Purchase #6	$190.45	8.480%	$206.6002	$206.60	$206.60	$206.60
Purchase #7	$12.67	3.860%	$13.1591	$13.16	$13.15	$13.20
7 purchase totals =	$812.72		$880.0227	$880.03	$880.05	$880.00