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	$54.54	12.440%	$61.3248	$61.32	$61.30	$61.30
Purchase #2	$96.93	8.188%	$104.8666	$104.87	$104.85	$104.90
Purchase #3	$155.64	13.515%	$176.6747	$176.67	$176.65	$176.70
Purchase #4	$239.98	11.546%	$267.6881	$267.69	$267.70	$267.70
Purchase #5	$152.42	8.469%	$165.3284	$165.33	$165.35	$165.30
Purchase #6	$140.57	11.124%	$156.207	$156.21	$156.20	$156.20
Purchase #7	$65.95	8.870%	$71.7998	$71.80	$71.80	$71.80
7 purchase totals =	$906.03		$1,003.8894	$1,003.89	$1,003.85	$1,003.90