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	$127.56	3.386%	$131.8792	$131.88	$131.90	$131.90
Purchase #2	$110.39	6.336%	$117.3843	$117.38	$117.40	$117.40
Purchase #3	$39.73	5.206%	$41.7983	$41.80	$41.80	$41.80
Purchase #4	$220.96	8.634%	$240.0377	$240.04	$240.05	$240.00
Purchase #5	$180.36	13.777%	$205.2082	$205.21	$205.20	$205.20
Purchase #6	$103.28	12.784%	$116.4833	$116.48	$116.50	$116.50
Purchase #7	$164.61	13.766%	$187.2702	$187.27	$187.25	$187.30
7 purchase totals =	$946.89		$1,040.0612	$1,040.06	$1,040.10	$1,040.10