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	$153.89	11.274%	$171.2396	$171.24	$171.25	$171.20
Purchase #2	$164.54	10.846%	$182.386	$182.39	$182.40	$182.40
Purchase #3	$102.81	6.111%	$109.0927	$109.09	$109.10	$109.10
Purchase #4	$80.78	7.454%	$86.8013	$86.80	$86.80	$86.80
Purchase #5	$6.98	11.643%	$7.7927	$7.79	$7.80	$7.80
Purchase #6	$181.70	4.831%	$190.4779	$190.48	$190.50	$190.50
Purchase #7	$73.72	4.208%	$76.8221	$76.82	$76.80	$76.80
7 purchase totals =	$764.42		$824.6123	$824.61	$824.65	$824.60