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	$37.86	11.488%	$42.2094	$42.21	$42.20	$42.20
Purchase #2	$69.60	11.541%	$77.6325	$77.63	$77.65	$77.60
Purchase #3	$49.86	4.676%	$52.1915	$52.19	$52.20	$52.20
Purchase #4	$55.72	7.422%	$59.8555	$59.86	$59.85	$59.90
Purchase #5	$203.82	9.247%	$222.6672	$222.67	$222.65	$222.70
Purchase #6	$151.26	11.191%	$168.1875	$168.19	$168.20	$168.20
Purchase #7	$148.56	13.819%	$169.0895	$169.09	$169.10	$169.10
7 purchase totals =	$716.68		$791.8331	$791.84	$791.85	$791.90