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	$78.29	6.627%	$83.4783	$83.48	$83.50	$83.50
Purchase #2	$174.59	11.610%	$194.8599	$194.86	$194.85	$194.90
Purchase #3	$196.74	13.543%	$223.3845	$223.38	$223.40	$223.40
Purchase #4	$145.99	13.869%	$166.2374	$166.24	$166.25	$166.20
Purchase #5	$39.49	11.270%	$43.9405	$43.94	$43.95	$43.90
Purchase #6	$35.44	7.413%	$38.0672	$38.07	$38.05	$38.10
Purchase #7	$178.44	6.461%	$189.969	$189.97	$189.95	$190.00
7 purchase totals =	$848.98		$939.9368	$939.94	$939.95	$940.00