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	$95.54	7.807%	$102.9988	$103.00	$103.00	$103.00
Purchase #2	$183.82	8.425%	$199.3068	$199.31	$199.30	$199.30
Purchase #3	$87.88	10.526%	$97.1302	$97.13	$97.15	$97.10
Purchase #4	$55.62	7.769%	$59.9411	$59.94	$59.95	$59.90
Purchase #5	$235.48	4.200%	$245.3702	$245.37	$245.35	$245.40
Purchase #6	$116.56	12.780%	$131.4564	$131.46	$131.45	$131.50
Purchase #7	$119.67	3.478%	$123.8321	$123.83	$123.85	$123.80
7 purchase totals =	$894.57		$960.0356	$960.04	$960.05	$960.00