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	$128.82	8.547%	$139.8302	$139.83	$139.85	$139.80
Purchase #2	$31.43	12.745%	$35.4358	$35.44	$35.45	$35.40
Purchase #3	$168.71	10.870%	$187.0488	$187.05	$187.05	$187.00
Purchase #4	$136.77	7.407%	$146.9006	$146.90	$146.90	$146.90
Purchase #5	$31.31	5.500%	$33.0321	$33.03	$33.05	$33.00
Purchase #6	$15.76	3.423%	$16.2995	$16.30	$16.30	$16.30
Purchase #7	$59.74	5.170%	$62.8286	$62.83	$62.85	$62.80
7 purchase totals =	$572.54		$621.3756	$621.38	$621.45	$621.20