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	$71.72	12.528%	$80.7051	$80.71	$80.70	$80.70
Purchase #2	$14.76	11.654%	$16.4801	$16.48	$16.50	$16.50
Purchase #3	$65.52	10.230%	$72.2227	$72.22	$72.20	$72.20
Purchase #4	$220.54	7.867%	$237.8899	$237.89	$237.90	$237.90
Purchase #5	$18.32	10.798%	$20.2982	$20.30	$20.30	$20.30
Purchase #6	$71.45	3.427%	$73.8986	$73.90	$73.90	$73.90
Purchase #7	$141.91	3.689%	$147.1451	$147.15	$147.15	$147.10
7 purchase totals =	$604.22		$648.6397	$648.65	$648.65	$648.60