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	$155.81	8.382%	$168.87	$168.87	$168.85	$168.90
Purchase #2	$232.55	10.107%	$256.0538	$256.05	$256.05	$256.10
Purchase #3	$139.99	10.817%	$155.1327	$155.13	$155.15	$155.10
Purchase #4	$93.32	6.626%	$99.5034	$99.50	$99.50	$99.50
Purchase #5	$229.71	3.746%	$238.3149	$238.31	$238.30	$238.30
Purchase #6	$151.81	9.267%	$165.8782	$165.88	$165.90	$165.90
Purchase #7	$198.53	8.641%	$215.685	$215.69	$215.70	$215.70
7 purchase totals =	$1,201.72		$1,299.4380	$1,299.43	$1,299.45	$1,299.50