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	$76.80	11.784%	$85.8501	$85.85	$85.85	$85.90
Purchase #2	$229.75	6.693%	$245.1272	$245.13	$245.15	$245.10
Purchase #3	$73.75	5.366%	$77.7074	$77.71	$77.70	$77.70
Purchase #4	$94.31	10.131%	$103.8645	$103.86	$103.85	$103.90
Purchase #5	$136.45	3.241%	$140.8723	$140.87	$140.85	$140.90
Purchase #6	$46.63	11.203%	$51.854	$51.85	$51.85	$51.90
Purchase #7	$126.43	4.348%	$131.9272	$131.93	$131.95	$131.90
7 purchase totals =	$784.12		$837.2027	$837.20	$837.20	$837.30