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	$85.88	4.290%	$89.5643	$89.56	$89.55	$89.60
Purchase #2	$234.67	13.250%	$265.7638	$265.76	$265.75	$265.80
Purchase #3	$58.67	7.457%	$63.045	$63.05	$63.05	$63.00
Purchase #4	$33.28	6.591%	$35.4735	$35.47	$35.45	$35.50
Purchase #5	$19.95	3.581%	$20.6644	$20.66	$20.65	$20.70
Purchase #6	$113.44	11.645%	$126.6501	$126.65	$126.65	$126.70
Purchase #7	$28.77	9.415%	$31.4787	$31.48	$31.50	$31.50
7 purchase totals =	$574.66		$632.6398	$632.63	$632.60	$632.80