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	$180.88	3.697%	$187.5671	$187.57	$187.55	$187.60
Purchase #2	$53.25	8.377%	$57.7108	$57.71	$57.70	$57.70
Purchase #3	$40.89	4.109%	$42.5702	$42.57	$42.55	$42.60
Purchase #4	$96.82	11.560%	$108.0124	$108.01	$108.00	$108.00
Purchase #5	$87.41	4.764%	$91.5742	$91.57	$91.55	$91.60
Purchase #6	$132.95	8.206%	$143.8599	$143.86	$143.85	$143.90
Purchase #7	$24.29	3.625%	$25.1705	$25.17	$25.15	$25.20
7 purchase totals =	$616.49		$656.4651	$656.46	$656.35	$656.60