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	$134.70	3.199%	$139.0091	$139.01	$139.00	$139.00
Purchase #2	$147.52	8.665%	$160.3026	$160.30	$160.30	$160.30
Purchase #3	$32.55	7.477%	$34.9838	$34.98	$35.00	$35.00
Purchase #4	$243.33	3.386%	$251.5692	$251.57	$251.55	$251.60
Purchase #5	$81.42	6.356%	$86.5951	$86.60	$86.60	$86.60
Purchase #6	$38.53	13.134%	$43.5905	$43.59	$43.60	$43.60
Purchase #7	$33.96	4.248%	$35.4026	$35.40	$35.40	$35.40
7 purchase totals =	$712.01		$751.4529	$751.45	$751.45	$751.50