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	$155.40	10.595%	$171.8646	$171.86	$171.85	$171.90
Purchase #2	$40.36	3.791%	$41.89	$41.89	$41.90	$41.90
Purchase #3	$162.38	3.658%	$168.3199	$168.32	$168.30	$168.30
Purchase #4	$147.81	9.295%	$161.5489	$161.55	$161.55	$161.50
Purchase #5	$106.85	5.792%	$113.0388	$113.04	$113.05	$113.00
Purchase #6	$13.59	11.410%	$15.1406	$15.14	$15.15	$15.10
Purchase #7	$137.50	3.284%	$142.0155	$142.02	$142.00	$142.00
7 purchase totals =	$763.89		$813.8183	$813.82	$813.80	$813.70