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	$37.94	11.559%	$42.3255	$42.33	$42.35	$42.30
Purchase #2	$71.40	5.758%	$75.5112	$75.51	$75.50	$75.50
Purchase #3	$136.51	13.443%	$154.861	$154.86	$154.85	$154.90
Purchase #4	$85.92	12.689%	$96.8224	$96.82	$96.80	$96.80
Purchase #5	$236.98	13.445%	$268.842	$268.84	$268.85	$268.80
Purchase #6	$157.46	4.532%	$164.5961	$164.60	$164.60	$164.60
Purchase #7	$213.93	12.364%	$240.3803	$240.38	$240.40	$240.40
7 purchase totals =	$940.14		$1,043.3385	$1,043.34	$1,043.35	$1,043.30