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	$164.32	9.273%	$179.5574	$179.56	$179.55	$179.60
Purchase #2	$35.91	12.322%	$40.3348	$40.33	$40.35	$40.30
Purchase #3	$201.96	5.744%	$213.5606	$213.56	$213.55	$213.60
Purchase #4	$34.26	3.383%	$35.419	$35.42	$35.40	$35.40
Purchase #5	$131.36	4.199%	$136.8758	$136.88	$136.90	$136.90
Purchase #6	$123.65	3.445%	$127.9097	$127.91	$127.90	$127.90
Purchase #7	$83.71	7.335%	$89.8501	$89.85	$89.85	$89.90
7 purchase totals =	$775.17		$823.5074	$823.51	$823.50	$823.60