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	$82.80	10.263%	$91.2978	$91.30	$91.30	$91.30
Purchase #2	$246.61	5.407%	$259.9442	$259.94	$259.95	$259.90
Purchase #3	$81.55	10.672%	$90.253	$90.25	$90.25	$90.30
Purchase #4	$47.32	7.611%	$50.9215	$50.92	$50.90	$50.90
Purchase #5	$129.34	8.368%	$140.1632	$140.16	$140.15	$140.20
Purchase #6	$202.88	11.799%	$226.8178	$226.82	$226.80	$226.80
Purchase #7	$126.28	9.229%	$137.9344	$137.93	$137.95	$137.90
7 purchase totals =	$916.78		$997.3319	$997.32	$997.30	$997.30