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	$127.61	9.258%	$139.4241	$139.42	$139.40	$139.40
Purchase #2	$84.83	7.614%	$91.289	$91.29	$91.30	$91.30
Purchase #3	$68.96	4.816%	$72.2811	$72.28	$72.30	$72.30
Purchase #4	$208.60	5.857%	$220.8177	$220.82	$220.80	$220.80
Purchase #5	$168.89	3.622%	$175.0072	$175.01	$175.00	$175.00
Purchase #6	$117.48	11.260%	$130.7082	$130.71	$130.70	$130.70
Purchase #7	$6.55	8.331%	$7.0957	$7.10	$7.10	$7.10
7 purchase totals =	$782.92		$836.6230	$836.63	$836.60	$836.60