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	$73.37	5.556%	$77.4464	$77.45	$77.45	$77.40
Purchase #2	$236.59	10.559%	$261.5715	$261.57	$261.55	$261.60
Purchase #3	$134.44	13.543%	$152.6472	$152.65	$152.65	$152.60
Purchase #4	$76.58	8.164%	$82.832	$82.83	$82.85	$82.80
Purchase #5	$90.68	13.118%	$102.5754	$102.58	$102.60	$102.60
Purchase #6	$41.57	8.649%	$45.1654	$45.17	$45.15	$45.20
Purchase #7	$181.32	8.308%	$196.3841	$196.38	$196.40	$196.40
7 purchase totals =	$834.55		$918.6220	$918.63	$918.65	$918.60