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	$55.32	6.340%	$58.8273	$58.83	$58.85	$58.80
Purchase #2	$28.53	9.753%	$31.3125	$31.31	$31.30	$31.30
Purchase #3	$242.87	9.448%	$265.8164	$265.82	$265.80	$265.80
Purchase #4	$161.48	4.812%	$169.2504	$169.25	$169.25	$169.30
Purchase #5	$226.93	3.342%	$234.514	$234.51	$234.50	$234.50
Purchase #6	$150.27	9.453%	$164.475	$164.48	$164.50	$164.50
Purchase #7	$46.33	4.310%	$48.3268	$48.33	$48.35	$48.30
7 purchase totals =	$911.73		$972.5224	$972.53	$972.55	$972.50