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	$26.58	7.472%	$28.5661	$28.57	$28.55	$28.60
Purchase #2	$103.33	8.220%	$111.8237	$111.82	$111.80	$111.80
Purchase #3	$21.79	3.519%	$22.5568	$22.56	$22.55	$22.60
Purchase #4	$242.48	11.163%	$269.548	$269.55	$269.55	$269.50
Purchase #5	$135.96	10.700%	$150.5077	$150.51	$150.50	$150.50
Purchase #6	$128.68	10.821%	$142.6045	$142.60	$142.60	$142.60
Purchase #7	$111.98	12.851%	$126.3705	$126.37	$126.35	$126.40
7 purchase totals =	$770.80		$851.9773	$851.98	$851.90	$852.00