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	$29.92	3.567%	$30.9872	$30.99	$31.00	$31.00
Purchase #2	$18.41	10.124%	$20.2738	$20.27	$20.25	$20.30
Purchase #3	$112.40	10.621%	$124.338	$124.34	$124.35	$124.30
Purchase #4	$215.42	8.567%	$233.875	$233.88	$233.90	$233.90
Purchase #5	$152.39	11.478%	$169.8813	$169.88	$169.90	$169.90
Purchase #6	$32.55	9.176%	$35.5368	$35.54	$35.55	$35.50
Purchase #7	$161.34	5.282%	$169.862	$169.86	$169.85	$169.90
7 purchase totals =	$722.43		$784.7541	$784.76	$784.80	$784.80