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	$27.84	11.402%	$31.0143	$31.01	$31.00	$31.00
Purchase #2	$79.55	5.535%	$83.9531	$83.95	$83.95	$84.00
Purchase #3	$27.42	5.400%	$28.9007	$28.90	$28.90	$28.90
Purchase #4	$180.54	6.579%	$192.4177	$192.42	$192.40	$192.40
Purchase #5	$172.65	13.760%	$196.4066	$196.41	$196.40	$196.40
Purchase #6	$128.89	7.302%	$138.3015	$138.30	$138.30	$138.30
Purchase #7	$125.56	5.547%	$132.5248	$132.52	$132.50	$132.50
7 purchase totals =	$742.45		$803.5187	$803.51	$803.45	$803.50