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	$127.33	12.257%	$142.9368	$142.94	$142.95	$142.90
Purchase #2	$71.96	9.751%	$78.9768	$78.98	$79.00	$79.00
Purchase #3	$82.31	13.455%	$93.3848	$93.38	$93.40	$93.40
Purchase #4	$247.74	5.689%	$261.8339	$261.83	$261.85	$261.80
Purchase #5	$47.71	4.138%	$49.6842	$49.68	$49.70	$49.70
Purchase #6	$209.86	8.322%	$227.3245	$227.32	$227.30	$227.30
Purchase #7	$152.89	7.643%	$164.5754	$164.58	$164.60	$164.60
7 purchase totals =	$939.80		$1,018.7164	$1,018.71	$1,018.80	$1,018.70