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	$58.64	3.452%	$60.6643	$60.66	$60.65	$60.70
Purchase #2	$191.68	10.338%	$211.4959	$211.50	$211.50	$211.50
Purchase #3	$179.33	11.257%	$199.5172	$199.52	$199.50	$199.50
Purchase #4	$62.49	7.778%	$67.3505	$67.35	$67.35	$67.40
Purchase #5	$231.37	5.134%	$243.2485	$243.25	$243.25	$243.20
Purchase #6	$159.79	3.172%	$164.8585	$164.86	$164.85	$164.90
Purchase #7	$39.46	7.391%	$42.3765	$42.38	$42.40	$42.40
7 purchase totals =	$922.76		$989.5114	$989.52	$989.50	$989.60