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	$249.70	6.612%	$266.2102	$266.21	$266.20	$266.20
Purchase #2	$99.73	12.618%	$112.3139	$112.31	$112.30	$112.30
Purchase #3	$172.81	11.421%	$192.5466	$192.55	$192.55	$192.50
Purchase #4	$39.86	4.865%	$41.7992	$41.80	$41.80	$41.80
Purchase #5	$63.63	13.617%	$72.2945	$72.29	$72.30	$72.30
Purchase #6	$247.40	9.143%	$270.0198	$270.02	$270.00	$270.00
Purchase #7	$160.63	9.808%	$176.3846	$176.38	$176.40	$176.40
7 purchase totals =	$1,033.76		$1,131.5688	$1,131.56	$1,131.55	$1,131.50