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	$83.82	7.412%	$90.0327	$90.03	$90.05	$90.00
Purchase #2	$73.36	13.547%	$83.2981	$83.30	$83.30	$83.30
Purchase #3	$32.61	8.853%	$35.497	$35.50	$35.50	$35.50
Purchase #4	$119.30	3.843%	$123.8847	$123.88	$123.90	$123.90
Purchase #5	$76.89	13.134%	$86.9887	$86.99	$87.00	$87.00
Purchase #6	$23.86	9.258%	$26.069	$26.07	$26.05	$26.10
Purchase #7	$129.69	13.776%	$147.5561	$147.56	$147.55	$147.60
7 purchase totals =	$539.53		$593.3263	$593.33	$593.35	$593.40