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	$74.69	5.177%	$78.5567	$78.56	$78.55	$78.60
Purchase #2	$155.28	12.714%	$175.0223	$175.02	$175.00	$175.00
Purchase #3	$144.51	12.475%	$162.5376	$162.54	$162.55	$162.50
Purchase #4	$14.46	7.384%	$15.5277	$15.53	$15.55	$15.50
Purchase #5	$201.73	4.202%	$210.2067	$210.21	$210.20	$210.20
Purchase #6	$95.39	4.451%	$99.6358	$99.64	$99.65	$99.60
Purchase #7	$20.88	7.245%	$22.3928	$22.39	$22.40	$22.40
7 purchase totals =	$706.94		$763.8796	$763.89	$763.90	$763.80