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	$242.86	11.273%	$270.2376	$270.24	$270.25	$270.20
Purchase #2	$156.72	9.853%	$172.1616	$172.16	$172.15	$172.20
Purchase #3	$235.76	12.512%	$265.2583	$265.26	$265.25	$265.30
Purchase #4	$160.85	4.773%	$168.5274	$168.53	$168.55	$168.50
Purchase #5	$219.39	12.407%	$246.6097	$246.61	$246.60	$246.60
Purchase #6	$245.72	12.112%	$275.4816	$275.48	$275.50	$275.50
Purchase #7	$41.94	9.711%	$46.0128	$46.01	$46.00	$46.00
7 purchase totals =	$1,303.24		$1,444.2890	$1,444.29	$1,444.30	$1,444.30