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	$72.82	9.684%	$79.8719	$79.87	$79.85	$79.90
Purchase #2	$22.65	12.476%	$25.4758	$25.48	$25.50	$25.50
Purchase #3	$222.59	3.560%	$230.5142	$230.51	$230.50	$230.50
Purchase #4	$117.43	11.330%	$130.7348	$130.73	$130.75	$130.70
Purchase #5	$206.39	7.767%	$222.4203	$222.42	$222.40	$222.40
Purchase #6	$173.36	9.528%	$189.8777	$189.88	$189.90	$189.90
Purchase #7	$187.96	11.499%	$209.5735	$209.57	$209.55	$209.60
7 purchase totals =	$1,003.20		$1,088.4682	$1,088.46	$1,088.45	$1,088.50