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	$17.46	3.222%	$18.0226	$18.02	$18.00	$18.00
Purchase #2	$83.30	3.677%	$86.3629	$86.36	$86.35	$86.40
Purchase #3	$168.52	10.496%	$186.2079	$186.21	$186.20	$186.20
Purchase #4	$185.82	5.768%	$196.5381	$196.54	$196.55	$196.50
Purchase #5	$84.51	7.151%	$90.5533	$90.55	$90.55	$90.60
Purchase #6	$170.36	10.604%	$188.425	$188.43	$188.45	$188.40
Purchase #7	$61.89	6.390%	$65.8448	$65.84	$65.85	$65.80
7 purchase totals =	$771.86		$831.9546	$831.95	$831.95	$831.90