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	$96.29	4.366%	$100.494	$100.49	$100.50	$100.50
Purchase #2	$75.89	12.551%	$85.415	$85.42	$85.40	$85.40
Purchase #3	$180.31	13.167%	$204.0514	$204.05	$204.05	$204.10
Purchase #4	$86.88	12.623%	$97.8469	$97.85	$97.85	$97.80
Purchase #5	$198.43	4.265%	$206.893	$206.89	$206.90	$206.90
Purchase #6	$59.68	11.692%	$66.6578	$66.66	$66.65	$66.70
Purchase #7	$243.34	12.410%	$273.5385	$273.54	$273.55	$273.50
7 purchase totals =	$940.82		$1,034.8966	$1,034.90	$1,034.90	$1,034.90