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	$55.56	12.319%	$62.4044	$62.40	$62.40	$62.40
Purchase #2	$59.56	7.323%	$63.9216	$63.92	$63.90	$63.90
Purchase #3	$37.72	6.660%	$40.2322	$40.23	$40.25	$40.20
Purchase #4	$139.94	3.847%	$145.3235	$145.32	$145.30	$145.30
Purchase #5	$104.77	7.424%	$112.5481	$112.55	$112.55	$112.50
Purchase #6	$14.42	3.539%	$14.9303	$14.93	$14.95	$14.90
Purchase #7	$199.50	11.591%	$222.624	$222.62	$222.60	$222.60
7 purchase totals =	$611.47		$661.9841	$661.97	$661.95	$661.80