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	$47.40	10.536%	$52.3941	$52.39	$52.40	$52.40
Purchase #2	$137.45	9.768%	$150.8761	$150.88	$150.90	$150.90
Purchase #3	$30.77	8.329%	$33.3328	$33.33	$33.35	$33.30
Purchase #4	$37.91	12.274%	$42.5631	$42.56	$42.55	$42.60
Purchase #5	$155.89	8.645%	$169.3667	$169.37	$169.35	$169.40
Purchase #6	$85.43	10.763%	$94.6248	$94.62	$94.60	$94.60
Purchase #7	$47.50	10.346%	$52.4144	$52.41	$52.40	$52.40
7 purchase totals =	$542.35		$595.5720	$595.56	$595.55	$595.60