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	$215.78	12.212%	$242.1311	$242.13	$242.15	$242.10
Purchase #2	$37.31	8.129%	$40.3429	$40.34	$40.35	$40.30
Purchase #3	$87.91	13.102%	$99.428	$99.43	$99.45	$99.40
Purchase #4	$196.36	4.116%	$204.4422	$204.44	$204.45	$204.40
Purchase #5	$11.53	13.790%	$13.12	$13.12	$13.10	$13.10
Purchase #6	$108.80	6.661%	$116.0472	$116.05	$116.05	$116.00
Purchase #7	$39.36	8.110%	$42.5521	$42.55	$42.55	$42.60
7 purchase totals =	$697.05		$758.0635	$758.06	$758.10	$757.90