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	$43.88	7.280%	$47.0745	$47.07	$47.05	$47.10
Purchase #2	$93.86	11.564%	$104.714	$104.71	$104.70	$104.70
Purchase #3	$171.35	3.203%	$176.8383	$176.84	$176.85	$176.80
Purchase #4	$136.26	6.304%	$144.8498	$144.85	$144.85	$144.80
Purchase #5	$231.46	5.595%	$244.4102	$244.41	$244.40	$244.40
Purchase #6	$82.27	9.315%	$89.9335	$89.93	$89.95	$89.90
Purchase #7	$25.65	10.443%	$28.3286	$28.33	$28.35	$28.30
7 purchase totals =	$784.73		$836.1489	$836.14	$836.15	$836.00