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	$122.48	11.582%	$136.6656	$136.67	$136.65	$136.70
Purchase #2	$212.31	12.357%	$238.5451	$238.55	$238.55	$238.50
Purchase #3	$157.27	7.553%	$169.1486	$169.15	$169.15	$169.10
Purchase #4	$77.72	6.614%	$82.8604	$82.86	$82.85	$82.90
Purchase #5	$69.25	5.261%	$72.8932	$72.89	$72.90	$72.90
Purchase #6	$90.94	8.634%	$98.7918	$98.79	$98.80	$98.80
Purchase #7	$131.39	10.741%	$145.5026	$145.50	$145.50	$145.50
7 purchase totals =	$861.36		$944.4073	$944.41	$944.40	$944.40