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	$244.98	11.482%	$273.1086	$273.11	$273.10	$273.10
Purchase #2	$106.35	5.548%	$112.2503	$112.25	$112.25	$112.30
Purchase #3	$113.31	6.730%	$120.9358	$120.94	$120.95	$120.90
Purchase #4	$181.73	3.256%	$187.6471	$187.65	$187.65	$187.60
Purchase #5	$189.83	12.682%	$213.9042	$213.90	$213.90	$213.90
Purchase #6	$250.39	12.128%	$280.7573	$280.76	$280.75	$280.80
Purchase #7	$137.89	12.634%	$155.311	$155.31	$155.30	$155.30
7 purchase totals =	$1,224.48		$1,343.9143	$1,343.92	$1,343.90	$1,343.90