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	$108.32	7.832%	$116.8036	$116.80	$116.80	$116.80
Purchase #2	$198.55	11.533%	$221.4488	$221.45	$221.45	$221.40
Purchase #3	$186.86	11.403%	$208.1676	$208.17	$208.15	$208.20
Purchase #4	$102.85	10.655%	$113.8087	$113.81	$113.80	$113.80
Purchase #5	$156.48	6.134%	$166.0785	$166.08	$166.10	$166.10
Purchase #6	$37.49	11.800%	$41.9138	$41.91	$41.90	$41.90
Purchase #7	$119.49	9.676%	$131.0519	$131.05	$131.05	$131.10
7 purchase totals =	$910.04		$999.2729	$999.27	$999.25	$999.30