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	$22.36	7.352%	$24.0039	$24.00	$24.00	$24.00
Purchase #2	$145.59	10.238%	$160.4955	$160.50	$160.50	$160.50
Purchase #3	$71.33	3.432%	$73.778	$73.78	$73.80	$73.80
Purchase #4	$111.40	7.557%	$119.8185	$119.82	$119.80	$119.80
Purchase #5	$140.98	6.473%	$150.1056	$150.11	$150.10	$150.10
Purchase #6	$17.73	4.832%	$18.5867	$18.59	$18.60	$18.60
Purchase #7	$89.99	12.339%	$101.0939	$101.09	$101.10	$101.10
7 purchase totals =	$599.38		$647.8821	$647.89	$647.90	$647.90