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	$125.56	11.330%	$139.7859	$139.79	$139.80	$139.80
Purchase #2	$127.75	7.150%	$136.8841	$136.88	$136.90	$136.90
Purchase #3	$247.89	10.370%	$273.5962	$273.60	$273.60	$273.60
Purchase #4	$29.82	12.280%	$33.4819	$33.48	$33.50	$33.50
Purchase #5	$192.50	4.585%	$201.3261	$201.33	$201.35	$201.30
Purchase #6	$57.70	3.170%	$59.5291	$59.53	$59.55	$59.50
Purchase #7	$115.61	12.168%	$129.6774	$129.68	$129.70	$129.70
7 purchase totals =	$896.83		$974.2807	$974.29	$974.40	$974.30