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	$19.31	13.392%	$21.896	$21.90	$21.90	$21.90
Purchase #2	$71.47	12.409%	$80.3387	$80.34	$80.35	$80.30
Purchase #3	$71.34	12.623%	$80.3452	$80.35	$80.35	$80.30
Purchase #4	$233.45	9.414%	$255.427	$255.43	$255.45	$255.40
Purchase #5	$26.61	6.544%	$28.3514	$28.35	$28.35	$28.40
Purchase #6	$33.41	10.421%	$36.8917	$36.89	$36.90	$36.90
Purchase #7	$32.39	8.663%	$35.1959	$35.20	$35.20	$35.20
7 purchase totals =	$487.98		$538.4459	$538.46	$538.50	$538.40