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	$128.91	6.281%	$137.0068	$137.01	$137.00	$137.00
Purchase #2	$92.62	5.196%	$97.4325	$97.43	$97.45	$97.40
Purchase #3	$27.88	7.217%	$29.8921	$29.89	$29.90	$29.90
Purchase #4	$6.81	8.515%	$7.3899	$7.39	$7.40	$7.40
Purchase #5	$125.82	4.256%	$131.1749	$131.17	$131.15	$131.20
Purchase #6	$73.90	6.123%	$78.4249	$78.42	$78.40	$78.40
Purchase #7	$82.64	4.156%	$86.0745	$86.07	$86.05	$86.10
7 purchase totals =	$538.58		$567.3956	$567.38	$567.35	$567.40