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	$64.98	11.547%	$72.4832	$72.48	$72.50	$72.50
Purchase #2	$99.95	11.596%	$111.5402	$111.54	$111.55	$111.50
Purchase #3	$5.25	13.661%	$5.9672	$5.97	$5.95	$6.00
Purchase #4	$164.85	13.223%	$186.6481	$186.65	$186.65	$186.60
Purchase #5	$93.28	8.740%	$101.4327	$101.43	$101.45	$101.40
Purchase #6	$24.54	7.539%	$26.3901	$26.39	$26.40	$26.40
Purchase #7	$7.85	6.826%	$8.3858	$8.39	$8.40	$8.40
7 purchase totals =	$460.70		$512.8473	$512.85	$512.90	$512.80