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	$147.44	13.594%	$167.483	$167.48	$167.50	$167.50
Purchase #2	$125.56	10.612%	$138.8844	$138.88	$138.90	$138.90
Purchase #3	$71.31	7.674%	$76.7823	$76.78	$76.80	$76.80
Purchase #4	$10.56	13.452%	$11.9805	$11.98	$12.00	$12.00
Purchase #5	$171.25	8.139%	$185.188	$185.19	$185.20	$185.20
Purchase #6	$177.96	5.557%	$187.8492	$187.85	$187.85	$187.80
Purchase #7	$141.50	12.290%	$158.8904	$158.89	$158.90	$158.90
7 purchase totals =	$845.58		$927.0578	$927.05	$927.15	$927.10