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	$229.48	9.371%	$250.9846	$250.98	$251.00	$251.00
Purchase #2	$80.46	3.176%	$83.0154	$83.02	$83.00	$83.00
Purchase #3	$179.70	11.792%	$200.8902	$200.89	$200.90	$200.90
Purchase #4	$152.84	10.418%	$168.7629	$168.76	$168.75	$168.80
Purchase #5	$49.69	8.637%	$53.9817	$53.98	$54.00	$54.00
Purchase #6	$162.84	6.870%	$174.0271	$174.03	$174.05	$174.00
Purchase #7	$137.90	12.554%	$155.212	$155.21	$155.20	$155.20
7 purchase totals =	$992.91		$1,086.8739	$1,086.87	$1,086.90	$1,086.90