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	$111.41	7.609%	$119.8872	$119.89	$119.90	$119.90
Purchase #2	$37.78	12.467%	$42.49	$42.49	$42.50	$42.50
Purchase #3	$48.72	4.577%	$50.9499	$50.95	$50.95	$50.90
Purchase #4	$24.62	3.731%	$25.5386	$25.54	$25.55	$25.50
Purchase #5	$225.58	6.525%	$240.2991	$240.30	$240.30	$240.30
Purchase #6	$6.35	4.569%	$6.6401	$6.64	$6.65	$6.60
Purchase #7	$148.53	9.494%	$162.6314	$162.63	$162.65	$162.60
7 purchase totals =	$602.99		$648.4363	$648.44	$648.50	$648.30