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	$201.33	12.661%	$226.8204	$226.82	$226.80	$226.80
Purchase #2	$84.56	5.868%	$89.522	$89.52	$89.50	$89.50
Purchase #3	$99.86	6.424%	$106.275	$106.28	$106.30	$106.30
Purchase #4	$177.27	12.396%	$199.2444	$199.24	$199.25	$199.20
Purchase #5	$157.41	12.758%	$177.4924	$177.49	$177.50	$177.50
Purchase #6	$109.82	12.673%	$123.7375	$123.74	$123.75	$123.70
Purchase #7	$42.30	12.181%	$47.4526	$47.45	$47.45	$47.50
7 purchase totals =	$872.55		$970.5443	$970.54	$970.55	$970.50