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	$25.51	7.566%	$27.4401	$27.44	$27.45	$27.40
Purchase #2	$79.55	4.369%	$83.0255	$83.03	$83.05	$83.00
Purchase #3	$210.59	7.803%	$227.0223	$227.02	$227.00	$227.00
Purchase #4	$74.83	4.646%	$78.3066	$78.31	$78.30	$78.30
Purchase #5	$150.67	11.354%	$167.7771	$167.78	$167.80	$167.80
Purchase #6	$48.92	9.454%	$53.5449	$53.54	$53.55	$53.50
Purchase #7	$228.48	5.849%	$241.8438	$241.84	$241.85	$241.80
7 purchase totals =	$818.55		$878.9603	$878.96	$879.00	$878.80