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	$19.71	9.296%	$21.5422	$21.54	$21.55	$21.50
Purchase #2	$33.61	5.350%	$35.4081	$35.41	$35.40	$35.40
Purchase #3	$42.45	7.148%	$45.4843	$45.48	$45.50	$45.50
Purchase #4	$190.56	12.660%	$214.6849	$214.68	$214.70	$214.70
Purchase #5	$249.69	4.544%	$261.0359	$261.04	$261.05	$261.00
Purchase #6	$33.39	12.314%	$37.5016	$37.50	$37.50	$37.50
Purchase #7	$168.34	4.215%	$175.4355	$175.44	$175.45	$175.40
7 purchase totals =	$737.75		$791.0925	$791.09	$791.15	$791.00