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	$72.89	12.755%	$82.1871	$82.19	$82.20	$82.20
Purchase #2	$85.38	9.755%	$93.7088	$93.71	$93.70	$93.70
Purchase #3	$199.30	11.181%	$221.5837	$221.58	$221.60	$221.60
Purchase #4	$37.54	10.197%	$41.368	$41.37	$41.35	$41.40
Purchase #5	$97.31	3.635%	$100.8472	$100.85	$100.85	$100.80
Purchase #6	$92.87	9.704%	$101.8821	$101.88	$101.90	$101.90
Purchase #7	$19.31	12.418%	$21.7079	$21.71	$21.70	$21.70
7 purchase totals =	$604.60		$663.2848	$663.29	$663.30	$663.30