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	$39.81	5.820%	$42.1269	$42.13	$42.15	$42.10
Purchase #2	$53.68	9.163%	$58.5987	$58.60	$58.60	$58.60
Purchase #3	$173.85	6.511%	$185.1694	$185.17	$185.15	$185.20
Purchase #4	$249.56	6.333%	$265.3646	$265.36	$265.35	$265.40
Purchase #5	$155.91	3.687%	$161.6584	$161.66	$161.65	$161.70
Purchase #6	$86.78	13.759%	$98.7201	$98.72	$98.70	$98.70
Purchase #7	$199.96	11.289%	$222.5335	$222.53	$222.55	$222.50
7 purchase totals =	$959.55		$1,034.1716	$1,034.17	$1,034.15	$1,034.20