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	$220.54	13.112%	$249.4572	$249.46	$249.45	$249.50
Purchase #2	$214.66	8.688%	$233.3097	$233.31	$233.30	$233.30
Purchase #3	$70.38	11.364%	$78.378	$78.38	$78.40	$78.40
Purchase #4	$102.59	11.139%	$114.0175	$114.02	$114.00	$114.00
Purchase #5	$46.55	11.601%	$51.9503	$51.95	$51.95	$52.00
Purchase #6	$17.90	3.394%	$18.5075	$18.51	$18.50	$18.50
Purchase #7	$213.97	6.411%	$227.6876	$227.69	$227.70	$227.70
7 purchase totals =	$886.59		$973.3078	$973.32	$973.30	$973.40