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	$215.98	4.555%	$225.8179	$225.82	$225.80	$225.80
Purchase #2	$164.88	8.124%	$178.2749	$178.27	$178.25	$178.30
Purchase #3	$136.46	8.599%	$148.1942	$148.19	$148.20	$148.20
Purchase #4	$142.63	12.800%	$160.8866	$160.89	$160.90	$160.90
Purchase #5	$27.50	13.203%	$31.1308	$31.13	$31.15	$31.10
Purchase #6	$65.39	9.829%	$71.8172	$71.82	$71.80	$71.80
Purchase #7	$58.77	4.133%	$61.199	$61.20	$61.20	$61.20
7 purchase totals =	$811.61		$877.3206	$877.32	$877.30	$877.30