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	$200.79	8.606%	$218.07	$218.07	$218.05	$218.10
Purchase #2	$47.67	9.480%	$52.1891	$52.19	$52.20	$52.20
Purchase #3	$191.86	11.134%	$213.2217	$213.22	$213.20	$213.20
Purchase #4	$120.82	12.791%	$136.2741	$136.27	$136.25	$136.30
Purchase #5	$65.41	9.813%	$71.8287	$71.83	$71.85	$71.80
Purchase #6	$50.55	4.594%	$52.8723	$52.87	$52.85	$52.90
Purchase #7	$37.68	12.859%	$42.5253	$42.53	$42.55	$42.50
7 purchase totals =	$714.78		$786.9812	$786.98	$786.95	$787.00