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	$101.44	11.306%	$112.9088	$112.91	$112.90	$112.90
Purchase #2	$76.83	7.269%	$82.4148	$82.41	$82.40	$82.40
Purchase #3	$212.41	9.437%	$232.4551	$232.46	$232.45	$232.50
Purchase #4	$48.30	13.279%	$54.7138	$54.71	$54.70	$54.70
Purchase #5	$187.62	9.591%	$205.6146	$205.61	$205.60	$205.60
Purchase #6	$72.59	7.508%	$78.0401	$78.04	$78.05	$78.00
Purchase #7	$180.66	10.526%	$199.6763	$199.68	$199.70	$199.70
7 purchase totals =	$879.85		$965.8235	$965.82	$965.80	$965.80