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	$142.36	13.180%	$161.123	$161.12	$161.10	$161.10
Purchase #2	$96.40	9.844%	$105.8896	$105.89	$105.90	$105.90
Purchase #3	$250.54	11.823%	$280.1613	$280.16	$280.15	$280.20
Purchase #4	$100.85	7.452%	$108.3653	$108.37	$108.35	$108.40
Purchase #5	$212.36	9.722%	$233.0056	$233.01	$233.00	$233.00
Purchase #6	$61.56	12.632%	$69.3363	$69.34	$69.35	$69.30
Purchase #7	$213.36	12.639%	$240.3266	$240.33	$240.35	$240.30
7 purchase totals =	$1,077.43		$1,198.2077	$1,198.22	$1,198.20	$1,198.20