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	$142.42	10.868%	$157.8982	$157.90	$157.90	$157.90
Purchase #2	$82.97	7.532%	$89.2193	$89.22	$89.20	$89.20
Purchase #3	$75.43	12.869%	$85.1371	$85.14	$85.15	$85.10
Purchase #4	$94.86	11.861%	$106.1113	$106.11	$106.10	$106.10
Purchase #5	$206.93	7.703%	$222.8698	$222.87	$222.85	$222.90
Purchase #6	$248.41	13.340%	$281.5479	$281.55	$281.55	$281.50
Purchase #7	$45.67	13.599%	$51.8807	$51.88	$51.90	$51.90
7 purchase totals =	$896.69		$994.6643	$994.67	$994.65	$994.60