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	$166.58	4.494%	$174.0661	$174.07	$174.05	$174.10
Purchase #2	$140.83	11.655%	$157.2437	$157.24	$157.25	$157.20
Purchase #3	$150.78	12.262%	$169.2686	$169.27	$169.25	$169.30
Purchase #4	$17.89	3.769%	$18.5643	$18.56	$18.55	$18.60
Purchase #5	$248.67	12.605%	$280.0149	$280.01	$280.00	$280.00
Purchase #6	$127.96	11.315%	$142.4387	$142.44	$142.45	$142.40
Purchase #7	$33.74	12.158%	$37.8421	$37.84	$37.85	$37.80
7 purchase totals =	$886.45		$979.4384	$979.43	$979.40	$979.40