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	$209.59	10.648%	$231.9071	$231.91	$231.90	$231.90
Purchase #2	$119.75	9.601%	$131.2472	$131.25	$131.25	$131.20
Purchase #3	$152.76	9.585%	$167.402	$167.40	$167.40	$167.40
Purchase #4	$135.77	10.828%	$150.4712	$150.47	$150.45	$150.50
Purchase #5	$95.52	7.379%	$102.5684	$102.57	$102.55	$102.60
Purchase #6	$22.51	12.226%	$25.2621	$25.26	$25.25	$25.30
Purchase #7	$170.41	6.510%	$181.5037	$181.50	$181.50	$181.50
7 purchase totals =	$906.31		$990.3617	$990.36	$990.30	$990.40