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	$173.57	8.670%	$188.6185	$188.62	$188.60	$188.60
Purchase #2	$69.32	12.182%	$77.7646	$77.76	$77.75	$77.80
Purchase #3	$56.36	6.119%	$59.8087	$59.81	$59.80	$59.80
Purchase #4	$155.36	12.220%	$174.345	$174.35	$174.35	$174.30
Purchase #5	$150.98	13.853%	$171.8953	$171.90	$171.90	$171.90
Purchase #6	$182.94	4.312%	$190.8284	$190.83	$190.85	$190.80
Purchase #7	$233.67	13.477%	$265.1617	$265.16	$265.15	$265.20
7 purchase totals =	$1,022.20		$1,128.4222	$1,128.43	$1,128.40	$1,128.40