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	$71.47	12.300%	$80.2608	$80.26	$80.25	$80.30
Purchase #2	$198.60	13.261%	$224.9363	$224.94	$224.95	$224.90
Purchase #3	$77.78	6.183%	$82.5891	$82.59	$82.60	$82.60
Purchase #4	$125.55	6.145%	$133.265	$133.27	$133.25	$133.30
Purchase #5	$195.44	4.188%	$203.625	$203.63	$203.65	$203.60
Purchase #6	$172.77	10.347%	$190.6465	$190.65	$190.65	$190.60
Purchase #7	$37.39	13.701%	$42.5128	$42.51	$42.50	$42.50
7 purchase totals =	$879.00		$957.8355	$957.85	$957.85	$957.80