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	$81.33	9.387%	$88.9644	$88.96	$88.95	$89.00
Purchase #2	$50.47	10.639%	$55.8395	$55.84	$55.85	$55.80
Purchase #3	$232.48	13.347%	$263.5091	$263.51	$263.50	$263.50
Purchase #4	$82.91	4.540%	$86.6741	$86.67	$86.65	$86.70
Purchase #5	$150.83	13.646%	$171.4123	$171.41	$171.40	$171.40
Purchase #6	$131.42	8.354%	$142.3988	$142.40	$142.40	$142.40
Purchase #7	$47.98	10.680%	$53.1043	$53.10	$53.10	$53.10
7 purchase totals =	$777.42		$861.9025	$861.89	$861.85	$861.90