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	$56.32	5.637%	$59.4948	$59.49	$59.50	$59.50
Purchase #2	$168.98	3.580%	$175.0295	$175.03	$175.05	$175.00
Purchase #3	$74.34	10.807%	$82.3739	$82.37	$82.35	$82.40
Purchase #4	$169.94	8.167%	$183.819	$183.82	$183.80	$183.80
Purchase #5	$83.47	9.752%	$91.61	$91.61	$91.60	$91.60
Purchase #6	$246.28	11.170%	$273.7895	$273.79	$273.80	$273.80
Purchase #7	$217.87	3.255%	$224.9617	$224.96	$224.95	$225.00
7 purchase totals =	$1,017.20		$1,091.0784	$1,091.07	$1,091.05	$1,091.10