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	$94.43	12.171%	$105.9231	$105.92	$105.90	$105.90
Purchase #2	$7.34	13.124%	$8.3033	$8.30	$8.30	$8.30
Purchase #3	$112.94	6.515%	$120.298	$120.30	$120.30	$120.30
Purchase #4	$218.89	7.295%	$234.858	$234.86	$234.85	$234.90
Purchase #5	$52.52	3.777%	$54.5037	$54.50	$54.50	$54.50
Purchase #6	$214.97	9.270%	$234.8977	$234.90	$234.90	$234.90
Purchase #7	$36.56	11.371%	$40.7172	$40.72	$40.70	$40.70
7 purchase totals =	$737.65		$799.5010	$799.50	$799.45	$799.50